A Child Shall Lead Them



""Woe to thee, O land, when thy king is a child, and thy princes eat in the morning!""

- The Bible

Youthful rulers are common in literature and history. If children, they are depicted as adorable; if in their teens or twenties, they simply create a sense of awe and protectiveness in their older advisers. Their naive simplicity may in fact make them good (and sometimes ruthless) rulers, as they prefer to cut through the red tape of court etiquette.

Because of their youth and inexperience, they are often underestimated by the villains, who are frequently Evil Uncles/Chancellors/Princes who were responsible for the assassination of the previous ruler, are currently in control, and do not intend to give it up. If the Queen Mother is regent, she is likely to over-control the young monarch and be unwilling to put down her power, though she is less likely to be actively evil.

They usually exhibit great wisdom in the course of the story, thus justifying their enormous power despite their youth. They may have friends (or adventures) among the servants or guards, giving them an insight into the lives of their subjects that their stuffy courtiers would scorn. They may have to resort to King Incognito to get anything done. Rebellious Princesses sometimes become good examples of this trope.

The Trope Namer is a line from Isaiah 11:6 in the Bible ("...and a little child shall lead them.")

May stem from the parent's having refused to leave In Its Hour of Need. (The child may have attempted to do the same, but forced to do so.)

Compare Royal Brat. Young Conqueror, The Wrongful Heir to The Throne The Evil Chancellor etc. may actively try to encourage this, and the young ruler must shake them off. The corporate version of this is the Grade School CEO, the petty leader Young and In Charge. If the entire government is children, not just one ruler, you're looking at a Teenage Wasteland.

Anime & Manga

 * By the end of Code Geass the world's power is wielded by three lolis teenage girls:
 * Tianzi, godhead-empress of China. She's just 13 years old and starts out as mix of puppet empress, White-Haired Pretty Girl and Lonely Rich Kid, therefore her bodyguard Li Xingke's ultimate goal is to give her the influence and power she needs to truly rule. He succeeds with help of Lelouch.
 * Kaguya Sumeragi, head of the influential Sumeragi House, High Chairman of the UFN and Japan's representative on said council despite being vaguely 14 or thereabout.
 * And in the Nightmare of Nunnally manga,  takes over the Empire at age 16.
 * Apparently the Europeans didn't want to be left out, because post-series supplemental material shows that they're also ruled by a teenage girl.
 * Actually, the trope best applies to the main protagonist of the series, Lelouch.  How's THAT?
 * Trinity Blood features two examples: His Holiness Alessandro XVIII, 399th Pope of Rome; and, Eternal Empress of the Methuselah Race. The former is respected by his citizens despite being a highly indecisive young boy; the latter is Really Seven Hundred Years Old but rules through a proxy so as to hide her child-like appearance.
 * Queen Mashiro of Mai-Otome is a Royal Brat at first, but becomes this after learning her lesson at the tender age of 14.
 * Integra in Hellsing started running the agency when she was still a young child. It helped that she also awakened Alucard.
 * The Dark King Ixpellia from Striker S Sound Stage X. The fierce, tyrant king of the Garea empire during the time of Ancient Belka. Oh, and she's a little girl in both appearance and personality, if not actual age.
 * Gaara from Naruto was elected as Kazekage of his village at some point during the timeskip, after which he is shown to be 15, in fact.
 * Tsunayoshi Sawada from Katekyo Hitman Reborn is chosen to be Boss of the most powerful Mafia family in Italy at only 14 years old. Likewise, his fellow boss Uni, who is even younger.
 * Shangri-La features the Metal Age group, which is taken over by Kuniko at eighteen. She might have done it earlier had she not been in jail for two years before the series due to being a domestic terrorist.
 * Played with in The Twelve Kingdoms. Shushou, the Queen of Kyou, became queen at age 12 to save her ravished lands... 90 years before the story starts. And she still looks like a teenage girl, since she stopped aging after she ascended to the trone.
 * A bit straighter in Youko's case, as she's as much 17 and has just become the Queen of Kei.
 * In Kyo Kara Maoh, the protagonist, Yuuri Shibuya becomes the ruler of the Great Demon Kingdom at the age of fifteen.
 * And lets not forget Small Shimaron's illustrious boy king, Saralegui.
 * Emperor Hotohori or Saihitei of Fushigi Yuugi is 17 years old at the time the series begins and the ruler of the Konan empire.
 * Don't forget  Reizeitei or Boushin, whom we see ruling when he's as much 10-12 years old.
 * One episode of Ghost in The Shell: Stand Alone Complex featured an improbable 12-year-old leader of a terrorist group.
 * Hitsugaya Toshiro, the captain of the 10th squad of the Gotei 13 in Bleach.
 * Kusajishi Yachiru, the vice-captain of the 11th squad as well.
 * Kimba the White Lion has the title character inherit his father's kingdom while still a cub after his parents died.
 * Gundam has a couple of these:
 * In Zeta Gundam and Gundam ZZ, the official leader of Axis/Neo-Zeon is Mineva Lao Zabi, seven year old sole survivor of the Zabi family, although it's pretty clear to everyone that her regent Haman Karn is the one with all the real power.
 * In Gundam Wing, Relena Peacecraft first becomes the sovereign of the Sanc Kingdom at age 15, then later Queen of the World. Though she doesn't hold the latter position for very long, she wields very real power while she has it.
 * Endless Waltz has Mariemaia, supposed daughter of Treize Kushrenada, leading her own army to conquer Earth in her preteens, although Dekim Barton is very clearly manipulating her actions and thoughts.
 * In Gundam SEED, Lacus Clyne (15) becomes the leader of her father's resistance movement following his death. By the end of Gundam SEED Destiny, she's the Chairwoman of the PLANT Supreme Council. Cagalli Yula Athha (same age) is also the chief representative of the nation of Orb following her father's death.
 * Endless Waltz has Mariemaia, supposed daughter of Treize Kushrenada, leading her own army to conquer Earth in her preteens, although Dekim Barton is very clearly manipulating her actions and thoughts.
 * In Gundam SEED, Lacus Clyne (15) becomes the leader of her father's resistance movement following his death. By the end of Gundam SEED Destiny, she's the Chairwoman of the PLANT Supreme Council. Cagalli Yula Athha (same age) is also the chief representative of the nation of Orb following her father's death.

Comic Books

 * Jenny Sparks, leader of The Authority, died with the 20th century; her successor, Jenny Quantum, was soon born, and adopted by the team's Official Couple. Eight years later, after everything had gone to hell in a handbasket, little Jenny Quantum got sick of watching the adults screw it up: she aged herself to 14, reassembled the team and has led them ever since.
 * The Sandman has a story-within-a-story about Prez Rickard, an 18-year-old who became president of the United States in an Alternate Universe. He does a perfect job for eight years, creates a golden age of peace and prosperity, and resists the temptation of Boss Smiley. Then he walks the earth until he dies and moves on.

Film

 * Queen Amidala. Though elected to the office of Queen (Naboo has a term-limited elected monarchy), she still wields an awful lot of power for a 14-year-old. Being an experienced senator by 24 was no mean feat, either, but then, her daughter was a senator by 19. Show-offs.
 * This seems to be regular practice on Naboo; Revenge of the Sith has a Queen who's supposed to be only 13 (who would've been elected at 12), and according to the Expanded Universe all politicians on Naboo retired at 20 until Palpatine refused to, and Padme was still unusual for staying in office into her twenties.
 * This would also probably explain why Naboo is the galaxy's buttmonkey.
 * Amidala was also elected as Princess of Theed (for totally unexplained reasons, Naboo's big on royal titles for elected offices; it's the equivalent of being mayor of the capital city) at an even younger age.
 * In the future of Idiocracy, the Secretary of Energy was in his early teens. Things like this happen when you give out Cabinet positions in a contest, though he didn't seem any worse at his job than anybody else.
 * Tropic Thunder. The heroin ring was run by a little kid, who was as ruthless as you'd expect a leader to be, and far more capable in combat than one would expect.
 * Robocop 2, very similarly, had a preteen end up in charge of a Nuke ring.
 * In the film version of Hitchhiker's Guide to the Galaxy, the leaders of Magrathea are this.
 * Actually, the are not in charge of Magrathea. They are merely their clients. They're also much older than they appear.

Literature

 * Duumvirate is absolutely packed with these, from the titular characters to lower-level Illuminati.
 * Royina Iselle from Curse of Chalion by Lois McMaster Bujold.
 * Emperor Gregor in Bujold's Vorkosigan Saga probably counts as well. He became Emperor--though with a Cincinnatus--at age four, took direct power at age twenty, and still had to put up with a handful of hopefuls for Evil Chancellor and pull one King Incognito before settling down to be a Reasonable Authority Figure.
 * In Deltora Quest, the heir to Deltora turns out to be only sixteen years old.
 * Dunevon, a minor character from Daughter of the Lioness, is only a toddler.
 * Graceling Bitterblue is about ten when she's crowned Queen of Monsea.
 * In Tanya Huff's Sing The Four Quarters, Lady Olinda sets up her nephew to be executed for treason so that she can control the new duc, his five-year-old son. The boy thwarts her in several ways before his father can reappear.
 * Elayne, Egwene, and Rand in Robert Jordan's The Wheel of Time
 * While they are still young, none of them are exactly children. Certainly not by the time they actually amass power.
 * Even if they all are technically adults(Elayne is 18, Egwene 18, and Rand 21), They've become the Amyrlin seat who even Kings bow to, The queen of a powerful country, and the freaking reincarnated savior of the human race leading upwards of 3 nations (Tear, Cairhien, somewhat Andor, Illian, Arad Doman, etc.)throughout much of the middle and later parts of the series. For being that young those are some pretty big accomplishments to put on people who wouldn't even be out of college yet.
 * A straighter example is Berelain, the first of Mayene, who isn't that old and has been ruling for a while when she's introduced.
 * Gorath from The Riftwar Cycle, or more famously the RPG Betrayal At Krondor, becomes tribe chieftain at age twelve, and in subsequent years restores his tribe to strength and avenges their earlier near-massacre. Particularly notable because he's a dark elf, and would normally need to be at least a century old to be considered more than Just a Kid, let alone lead.
 * In Katharine Kurtz's Deryni series, Kelson Haldane inherited the throne at the age of thirteen, and was crowned the day after his fourteenth birthday.
 * King Javan Haldane, from the prequel series- too bad he has an Evil Chancellor.
 * Several from A Song of Ice and Fire: Danaerys Targaryen, Robb Stark, and Brandon Stark, all of whom are well-meaning and even effective but naive, and Joffrey Baratheon, who's a major subversion regarding the goodness part. He's later replaced by little brother Tommen, who's very kind-hearted but really too young to be anything but a puppet for his mother, Cersei.
 * And Lord Robert Arryn, who's six years old and willing to throw someone off a cliff on hearsay evidence.
 * Lord Bolton describes boy lords as the bane of any house, and a desire to avoid one is his reason for making Ramsay his heir instead of having another son. The fact that Ramsay is completely Ax Crazy and would almost definitely run House Bolton right into the ground if left in charge seems to have escaped him.
 * Michael Karl in Andre Norton's The Prince Commands.
 * All four of Fiona Patton's Historical Fantasy Branion Realm series feature young royals and sovereigns as protagonists, often leading armies. In the first book, the ruler is 24, and much younger for large parts of the book; his mother took the throne at 25, and led a "Charge of Carnage" at 14. In the second, the ruler is five; her two immediate predecessors both took the throne at age 10. In the third, the ruler is 18, and was twelve when he cunningly poisoned an entire enemy army.
 * The Boy Emperor of the Agatean Empire in Mort, who sucessfully poisons his Evil Chancellor and former tutor with the dish the chancellor prepared for him ("I had a good teacher.") Apparently later killed by his uncle, the Royally Screwed-Up emperor in Interesting Times.
 * Teppic is still a teenager in Pyramids (just graduated from the Assassins' Guild) when he ascends to the throne of Djelibeybi.
 * Xuan at the end of Lords of the Bow is proclaimed Emperor of the Chin at the age of seven, after Zhi Zhong murders his father.
 * When Luxa is introduced in The Underland Chronicles, she's eleven, and the Queen of Regalia.
 * The Chronicles of Narnia primarily have the Pevensie siblings who lead Narnia's Golden Age starting when they were 13 (Peter), 12 (Susan), 10 (Edmund) and 8 (Lucy). Likewise, Caspian is 13 when he takes the throne.
 * At the end of The Obsidian Trilogy, we get the electoral version of this trope.
 * Also, in Stephen King's "Children of the Corn", the group is led by then-nine-year-old Isaac.
 * At the end of Deltora Quest series one, Lief of Del takes the throne. He's sixteen, and thinks more with his heart than with his brain... and yet, because the books were inspired by JRPGs of the mid-1990s, this ends well.
 * Not quite. He's still a child, but he did grow over the story to understand that there was a time and place for emotions to rule. He thinks with both his heart and his clever mind. And, by the end of the series,he's 18, and has learned even more about evil, temptation, and duty.
 * The Childlike Empress from The Neverending Story appears to follow this trope, but in fact, she is the oldest being in Fantastica, as old as imagination itself, and her childish appearance being just as her name shows.
 * Paul Atreides in Dune
 * His father Leto Atreides became Duke at 14 after the death of his father Paulus in a bull-ring. He rules justly and fairly.
 * His first order of business? Banish.
 * And Paul's children technically inherit the throne shortly after being born, but their aunt Alia rules as regent until Leto II seizes control when he's about 12.
 * In Harry Harrison's Bill the Galactic Hero novel, the fleet admiral is an infant. His unintelligible utterings and cries are "translated" by his nannies into orders. No wonder the humans are having such a hard time beating foot-tall lizards. Then again, that entire universe runs on the Rule of Funny.
 * In Sergey Lukyanenko's Morning Nears, Marcus is a teenage bastard son of the ruler of the State with no claim to the throne. However, when it becomes clear that he may be the next messiah, everyone around him begins to think of him as their new ruler, which he will be once he gains enough supporters by making miracles. His father will be forced to abdicate.
 * In Edgar Rice Burroughs's The Mad King, the boy king had been imprisoned for ten years as he had lost his wits. His uncle, appointed Regent, said so.
 * After Emperor Justinian was blinded in a coup attempt a third of the way through The Belisarius Series, Empress Theodora avoided a succession crisis by adopting the eight year old son of her best friend (who, incidentally, also happened to be the stepson of the Roman Empire's best general) and putting him on the throne. Of course setting herself up Empress Regent and naming her husband Grand Justicar were not to be sneezed at.
 * The Kid Who Ran For President by Dan Gutman
 * Jenna is only ten years old when she is called to rule over the Castle in Septimus Heap.
 * Evading this is part of the background if the Codex Alera series, as 's status as   is deliberately hidden for as long as possible to give him time to develop the skills he would need as ruler. By the time he learns his true name is , he's already had a full education at the most prestigious university in the nation, trained as a spy and assassin, and commanded a field army against impossible odds fighting an immense army of centuries old, two-meter tall wolfmen and won. By the time he's in a position to lead, he's managed to reach his mid-twenties.
 * The entire point of Ender's Game by Orson Scott Card is to train Andrew "Ender" Wiggin (who is a six-year-old boy at the start of the novel) to command humanity's forces in a Bug War. Apparently, Ender's older brother Peter and sister Valentine are just as smart as him, but they don't appear to have the qualities the fleet requires. Peter has all the makings of a serial killer (he psychologically tortures Ender and Valentine and disects squirrels while they're alive), and Valentine has too much empathy for war. While Ender is at Battle School, Peter convinces Valentine to help him take over the world in order to prevent another world war, which is sure to start as soon as the buggers are defeated. They create online personalities called Locke (Peter) and Demosthenes (Valentine), which argue competings points with the eventual goal of having Locke having so much influence he can write policy for the entire world. By that point, the truth that they're really children will be known, but no one will care. And yes, this is exactly what happens. A short war breaks out after Ender beats the buggers (before he's 16), and Peter manages to stop it and is made Hegemon of Earth shortly after. Valentine's (or rather Demosthenes's) writings are still read and discussed thousands of years later. Oh, and Ender also manages to inadvertantly start a new religion before he's 20.
 * David Inarai became the king in the land he and his mother created.
 * In Jack Vance's Planet of Adventure series: Traz. The nomad tribes' nominal leaders are generally teens or pre-teens--probably so the priests, who are the actual leaders, can have an easier time.

Live Action TV

 * The Anointed One in Buffy the Vampire Slayer. The Master actually quotes the name of this trope.
 * In the Bad Future of the first Legend of the Seeker season finale, the preteen son of Darken Rahl and Kahlan Amnell (who was forced to marry Rahl after Richard's apparent death), is a self-made orphan after executing his mother (for attempting to kill him) and confessing a guard to kill his father. He then proceeds to confess the entire population of D'Hara and beyond, ensuring ultimate loyalty.
 * Pair of Kings the twin brothers Boomer and Brady are both crowned as kings of an island called Kinkow.

Music

 * Vocaloid's Story of Evil series of songs features Rin as a fourteen-year-old ruling princess. The result is definitely not pretty.

Religion and Mythology

 * The Bible provides the page quote. The Trope Namer is an unrelated but famous passage about the Messiah.
 * Judah had several child rulers, such as Joash, crowned at 7, and Josiah, crowned at 8. They were some of the few kings who "did what was right in the eyes of the Lord"
 * By most sources, King Arthur was somewhere in the 15-to-18 range when he was crowned High King. The other rulers were not happy.

Tabletop Games

 * Jaela "Loli-Pope" Daran, the 11-year-old head of the Church of the Silver Flame in the Eberron setting for Dungeons and Dragons. She started at 6.
 * Elisabetta Barbados, the 13 year-old Holy Sacred Empress of Abel in Anima Beyond Fantasy. In fact, she's known as the Child Empress.

Theatre
""Henry VI, in infant bands crowned King/Of France and England, did this king succeed/Whose state so many had the managing/That he lost France, and made his England bleed." (epilogue, Henry V)"
 * Shakespeare's Henry VI (also a historical figure) was crowned king at nine months old, after Henry V died. This is an instance of a child king being portrayed as wholly negative, as he is too young and unknowledgeable to keep his courtiers from the petty in-fighting. Because he has no father to guide him, Henry stays weak and naive, which eventually leads to the War of the Roses.


 * Antony and Cleopatra: Octavius Caesar, though older than most examples, is noted in play by various characters for only being in his twenties and ruling Rome.

Video Games

 * Prince Roan from Grandia II. Who spends most of his time as a main character in the hero's party and who continues to fight with them even after circumstances have forced him to take the throne.
 * In Final Fantasy Crystal Chronicles: My Life as a King, you play as a 10-year-old king who took the throne after his father's disappearance.
 * Final Fantasy XII had Larsa Solidor who was picked to be the next emperor by his dying father because his older brother Vayne was Obviously Evil. Once both his brother and father realized that the Evil Chancellors would try to manipulate him they decided to have Vayne murder dear old dad and frame the council in order to protect him. Which caused Larsa to not become the emperor until the very end of the game.
 * In Final Fantasy VIII, Balamb Garden trains students from the age of 5 to become mercenaries, with several students taking on positions of leadership by the time they reach their late teens. The results of this practice are VERY mixed. It eventually turns out that the reason for this practice is because
 * Final Fantasy IX had Princess Garnet, who turned 16 at the start of the game and by the end,
 * Final Fantasy Tactics had Princess Ovelia, and Prince Orinas, each set up with a regent and sent to lead troops. Ovelia was not quite 18 at the time, while Orinas was 2.
 * Though the game kept an active calendar, and with a little grinding, you could age the boy prince into his teens, twenties, or even sixties, thus destroying the story.
 * is installed as a puppet ruler in Suikoden V. Unfortunately, even though the bad guys keep her aide hostage as leverage, they don't count on her actually exerting her power as Queen.
 * Laharl of Disgaea Hour of Darkness.
 * World of Warcraft had Anduin Wrynn lead Stormwind while his father was missing in action. He was assisted by Lady Katrana Prestor and Highlord Bolvar Fordragon.
 * Not really, while he was indeed the offical ruler everyone knew that he was more or less balantly controlled by his advisors... And Bolvar usually defered to Lady Katrana . It's a classic-era storyline
 * In first part of Virtual Villagers, the birth of the Golden Child signals a new era for the villagers, as he guides them to a new area on the island (continuing on the next game).
 * Fire Emblem: Path of Radiance and Radiant Dawn had Sanaki, the 10- to 13-year-old empress of Begnion.
 * One of the rare villainous examples is Price Yurius from Seisen no Keifu, who at the tender age of 15 is pretty much the one holding the power instead of . He also directs the horrible   and is the Dragon-in-Chief to Big Bad Manfloy.
 * There's also Leaf, who at age 16 is the leader of a resistence army in Thracia 776 and then joins Celice's own group. If he makes it to the end, he becomes the King of Lester and rules peacefully alongside his sister Altenna (who is just 20) and his also-around-16 girlfriend/wife.
 * The mechanics of succession in Imperium Nova can cause this to happen. Most notable is Hogan Galle, who became head of house at age five, head of faith at age eight, and emperor of the galaxy at age fourteen.
 * The basic plot of Little Kings Story is this.
 * Cardith Lorda from the Civilization IV mod Fall From Heaven II.
 * Prophet Cha Dawn of the Cult of Planet in Sid Meier's Alpha Centauri.
 * Several shorts by Michael Ely, one of the game's writers, have Cha Dawn being carried into battle on shoulders.
 * Fon Master Ion, who is roughly fourteen, is head of the religion that governs the entire world. The also counts.
 * In the Medieval installments of the Total War games, it is entirely possible, through extremely nasty bad luck, to end up with a fourteen-year old king/sultan. This usually only happens if all other eligible faction heirs get killed and the king kicks the bucket, leaving only a young, untested son as the last available option. Alternately, the king could be batty and simply designate the boy as his heir over more eligible options because he's completely nuts. If the king is really nutty, the heir won't be a blood relation but a captain who was adopted as a son after he killed a single-unit company of brigands.
 * In Drawn: Dark Flight, your ultimate goal is to drive out the shadows over the kingdom so that the child Iris can take her place as rightful ruler.

Web Original

 * In The Gamers Alliance, Gerard Aurelac becomes the King of Maar Sul in his early teens and comes up with a plan to capture Pronin whose forces are besieging Maar Sul City in the Godslayer era.

Western Animation
"Tygra: You may be king, but I'm still older than you."
 * Prince Pyrus of Shadow Raiders rules over an entire planet.
 * 13-year-old Elyon Brown aka Queen Elyon from WITCH becomes this after a brief stint as a Dark Magical Girl.
 * As of the finale of Avatar: The Last Airbender,
 * According to the website, the Earth King took the throne at the age of four. Unfortunately, Long Feng took advantage of this.
 * In ThunderCats (2011) Thundera's King Lion-O, at seventeen is the youngest of the Blue Bloods in his group of Thundercats. When Old Soldier Panthro joins, he dryly lampshades their lack of "adult supervision" prior to his arrival, while Lion-O's adoptive brother Tygra makes his age the subject of petty insults.


 * On Young Justice, the queen of Vlatava is a ten-year-old girl named Perdita.

Real Life

 * France's Louis VII, IX, XIII, XIV and XV. Also Charles VI, VIII and IX. And to top it off, John I, who became king at birth... and died just five days later.
 * King Baldwin IV of the Crusader Kingdom of Jerusalem was only 13 when crowned and even then he proved to be an effective leader. At age 16, he gave the Crusaders a decisive victory in the Battle of Montgisar against Saladin, who barely managed to escape. Had he not been a victim of leprosy, perhaps the crusader states would have lasted longer than they did.
 * England's Henry III, Edward III, Richard II, Henry VI, Edward V and Edward VI.
 * Scotland's Mary I (Mary, Queen of Scots) and her son James VI, who would become James I of England. James got the Scottish throne after his mother was overthrown and was only thirteen months old. Mary's father died of what was probably cholera and she became Queen at six days old.
 * This was actually a pattern in the Scottish Royal House. Of James I through James V inclusive, the oldest at his accession was 15.
 * Margaret of Norway, was seen by many to be the queen of Scots from 1286 until her death in 1290. It should be noted that she died at age seven.
 * Joan of Arc, patron saint of France, was granted command of the French army at the tender age of 16. Under her leadership, the long string of English victories came to an abrupt halt. No wonder the English were so eager to see her removed when she was captured.
 * Egypt's King Tutankhamen, who became Pharaoh when around 8 and died at age 18.
 * Egypt's Pepi II Neferkare (reigned 2278?-2184 BC) came the throne at the age of 6 and died 94 years later.
 * The exact length of his reign is disputed, and was probably only 64 years.
 * Elagabalus, emperor of Rome, is perhaps the other side of this trope, doing everything with his power you would expect of a sex-crazed teenager with a short attention span. Hence, a Royal Brat. He was murdered by the Praetorian Guard 4 years after taking the throne at the age of 14.
 * He was subsequently succeeded by his cousin, 14-year old Alexander Severus.
 * Charles XII of Sweden took the throne fairly at 14 and was just 18 years when he won the Battle of Narva (some historians claim his aides deserve more credit for that particular battle, no matter). He was more effective then many young rulers as he was a fairly good Strategist. However his recklessness and weakness in long-term planning kept him from rising to the level of a Wise Prince.
 * Mehmed II of the Ottoman Empire took Constantinople at the age of about nineteen.
 * Joan I of Navarre, who became queen of Navarre and countess of Champagne at the age of three.
 * Jadwiga/Hedwig of Anjou, King of Poland. She (that's right, she) became king at the age of ten, and became something of a Wise Princess.
 * The last emperor of China, Puyi, ascended the throne when he was three. Child emperors were a favorite political tool for ambitious courtesans, as they were too young (and spoiled) to rule effectively. The early chapters of Romance of the Three Kingdoms chronicles the (fictionalized) account of such a succession of ridiculously young emperors. The Emperor Kangxi, however, ascended the throne at the tender age of eight, and his reign was widely considered to be the Qing dynasty's golden era.
 * Emperor Kangxi's father, Emperor Shunzhi was only five years old when he ascended the throne.
 * This was pretty common in medieval Muslim kingdoms. An atabeg (literally "father-prince" in Turkish, but more like godfather/stepfather) was sometimes appointed to teach and assist a minor on the throne. Eventually, atabeg became a hereditary title roughly equivalent to duke or somesuch. The most famous hereditary atabegs are the Zengids, the rulers of Mosul; they are directly responsible for the Second Crusade (thanks to their pressure on the Kingdom of Jerusalem) and indirectly responsible for the Third (Saladin was their trusted lieutenant who took over Egypt for them; he quickly exploited the fact that the atabeg was a minor (!) to consolidate control over Greater Syria as well.
 * Christina of Sweden became king of Sweden when she was six years old. She took the oath as king, not queen, and was nicknamed 'the Girl King'.
 * In 1867, 14-going-to-15 Crown Prince Mutsuhito took over the reins of Imperial Japan after the death of his father. He would be known in history as the one who started the Empire's renovation (for some, a Magnificent Bastard; for others, a Smug Snake with good PR and effective counselors)... Emperor Meiji.
 * Actually, many Japanese emperors were like this, such as the eight-year-old Antoku from the Tale of the Heikei. It was practice for hundreds of years to keep very young men on the throne so that the real ruling of the country was left to the members of the Fujiwara clan, serving as regents, who also married their children into the line whenever possible. Many emperors abdicated early, and took on more power and authority as "retired emperors" while their younger successors were kept cloistered. And, of course, for about two hundred years during the Warring States period the real power fell to whomever was Shogun just then.
 * The children's crusades, both led by young teenage boys with great expectations. Suffice to say that they didn't turn out so well.
 * Russia's Ivan the Terrible (sixteen at the start of his reign), Mikhail Romanov (also sixteen), Peter the Great (ten) and Peter II (eleven, died at fourteen). The most extreme Russian example is Ivan VI: enthroned at the age of eight weeks, overthrown little more than a month later, imprisoned for the rest of his life, killed nearly a month before his 24th birthday.
 * The Sassanid Empire took this trope to the Logical Extreme when Shapur II became the only known monarch to be crowned in utero. In other words, while his mother was still pregnant with him, a coronation ceremony was held and the crown was placed on her belly, making him the next ruler.
 * A similar case occurred in Spain with Alfonso XIII, who became king at birth.
 * Here's a question: What if he'd been female? In Spain that wouldn't have been a problem (Alfonso's grandma had been the reigning queen Isabella II), but the rules did not allow that in Sassanid Persia.
 * It would have also been an issue in Spain at the time. Had he been born a female and the rightful ruler more than 200 years prior, it would have been fine..but when Alfonso's ancestor came to the throne from France as Philip V, he introduced France's Salic Law to Spain. Isabella II's father needed special and highly controversial legislation to allow her to become ruler in the first place, and it was a major reason for the revolution that eventually deposed her. Making it more of an issue is that while there was a powerful faction in Spanish politics at the time who wanted to make the monarchy into what it basically is today, it was far from certain that they would win.
 * There were two Sassanid empresses, Borandohkt and Azarmidokht, that ruled, albeit briefly, in the 7th century.
 * Jean-Claude "Baby Doc" Duvalier, son of François "Papa Doc" Duvalier, became President of Haiti at the age of 19.
 * Dom Pedro II, Emperator of Brazil, was crowned at age fifteen after long, hard years of studies and training for assuming the charge. Nearly 60 years later, he became perhaps the most popular monarch ever to be overthrown. It's said that the only person in Brazil other than those responsible for the coup who didn't mind was Pedro himself, who'd grown tired of ruling. The citizens were pissed at how he was treated.
 * King Oyo of Toro is a modern-day example. Though he's technically an adult now, he was crowned at age 3 1/2.
 * William the Bastard not only had to deal with becoming the Duke of Normandy at 7 years old, as his name obviously implies, he was the bastard son of a tanner's daughter. As such, he dealt with multiple attempts on his line and his title, but he made it into his teens, was knighted by the King of France at 15, and by 19, was routinely seeing off all his rivals on the battlefield. Unlike most child rulers, William acheived great heights, the most notable of course being the defeat of King Harold Godwinson of England and taking the throne himself.
 * Sobhuza II of Swaziland ascended to the throne at the age of six months on the 10th of December, 1899, and reigned until his death 82 years, 254 days later, in 1982, making his reign the longest reign of recent history, and the third longest of all time.