Yes, Virginia

In an episode with this plot, one character (typically a child or very naive/innocent person) will believe in Santa. At least one other character will try to prove to them otherwise, but by the end of the episode Santa's existence is confirmed.

It will never be explained why all the presents appearing without anyone buying or wrapping them is not considered convincing evidence in these settings. Quite often it doesn't seem to happen; even though Santa is making deliveries all over the world, no one ever gets any extras unless it's a plot point.

Compare Real After All, How Can Santa Deliver All Those Toys.

Anime & Manga

 * Subverted in Magical Girl Lyrical Nanoha, Nanoha tells Fate about Santa, hoping that she might believe in him for a little while, but is unsuccessful when Fate begins questioning certain aspects of the Santa fairytale, like how he can fly. Nanoha notes that few kids believe in Santa in their modern society, that Arisa and Suzuka never believed him, and that her older sister Miyuki believed in him until 4th grade.
 * In The All-New Tenchi Muyo! manga series, Washu goes to great lengths to make sure other kids doesn't destroy Sasami's perspective of Santa - mostly by teleporting items (or the other girls). In the end, it's all for naught: Sasami still believes in Santa, knows there are kids who don't - she says that's why the parents give kids Christmas presents instead of Santa!

Comic Books

 * Spoofed in a four page story in the DCU Infinite Holiday Special: Superman reads a child's letter asking for Santa and decides to dress up like Santa to prove he's real. Batman stops him and tells him how silly that is and that he should be helping people...which is all a ruse so he can dress up like Bat-Santa! It ends with Superman decking Bat-Santa.
 * Wow...that just says so much about Superman.
 * A better example happens in an issue of DC Comics Presents, where Superman tries to foil one of The Toyman's plots on Christmas Eve but temporarily loses the power of flight. He runs into Santa Claus at the North Pole, who gives him a ride and helps defeat the villain. In the end, it seems it was All Just a Dream... and then Superman finds his favorite childhood toy, that was destroyed when Krypton exploded!
 * this is all a moot point anyway, as Santa is a confirmed entity in the DC universe. he fights his way into Apokolips every year to give Darkseid a chunk of coal.
 * And then there's the Marvel story Yes, Virginia, There Is A Santron, where Gadgeteer Genius Virgie Hanlon, a young woman who never got over being told by classmates that Santa wasn't real when she was 8 decides to build a robot Santa. Unfortunately, unknown to her, the parts she used belonged to Ultron and "Santa" unsurprisingly immediately runs away to attack the Avengers. Luckily, Virgie's programming compels "Santron" to eat cookies and thus he is easily defeated. It ends on this Crowning Moment of Heartwarming.

Film

 * Miracle On 34th Street, based on the famous editorial. The kid in question doesn't believe because her mother thinks that it's not proper to believe in someone that she doesn't think exists.
 * The Santa Clause has elements of this. Scott Calvin pretends to believe in Santa for Charlie's sake, but once Santa actually shows up, he desperately tries to find a more plausible explanation for what's going on, breaking the ruse. Later, Charlie's mother and step-father get to discover for themselves that Santa is real.
 * In Santa's Slay, Santa says "yes, Virginia, there is a Santa Claus" to a woman surprised by him breaking into the house.
 * Interestingly enough, Santa Claus Conquers the Martians averts this from the start - Santa's existence is a known fact, and the movie even opens with a reporter visiting the workshop and interviewing him. This isn't a good thing, because Aliens Steal Cable...
 * Likewise, The Nightmare Before Christmas also averts this by having Santa's existence be an known fact, even cancelling Christmas when Santa can't be found.
 * So why didn't they know about his Halloween equivalent, Jack Skellington?
 * "There are few who'd deny, at what I do I am the best\For my talents are renowned far and wide . . . To a guy in Kentucky, I'm Mister Unlucky/And I'm known throughout England and France!" They know about Jack, all right, they just didn't realize it was him taking over Christmas.

Literature

 * The classic children's book The Polar Express (recently made into The Film of the Book).
 * Parodied on the back of O Ye Jigs and Juleps
 * Subverted in Superfudge, where Peter has never believed in Santa (he caught his parents stacking presents under the tree when he was three) and only humors Fudge under orders from their parents. Fudge goes into ecstasies over his new bike on Christmas morning, thanking Santa "wherever he is", but confides to Peter that he's never believed, either.
 * The Ingalls family had to do a lot of explaining to their kids about whether Santa Claus was going to make it out to whatever new, barely-settled territory they were living in that year, and if so how, and how much to expect. In one book, when the upcoming Christmas is looking pretty sparse, Ma tells Laura and Mary that they should have realized by now that Santa can't be just one person who goes around to each individual house -- but he's omnipresent and magical and manifests in unselfishness, so she thinks it would be nice if this year instead of presents for themselves they only wished for new horses for their father. In the end they do get a little candy along with the horses and their presents for each other.
 * Spoofed in Hogfather: '...yes, Twyla: there is a Hogfather.' Of course, the Hogfather does exist, and Susan's preceding speech was about how people are credulous and childish anyway, so this is something of a subversion...

Live Action TV
"Andy Hamilton: The Sun was very irresponsible, though, because there was a very alarmist headline, which said, Santa and Four Elves Beaten Up. And I think we should say, to any small children watching, Santa is okay.
 * Family Matters
 * The George Lopez Show
 * The Nanny did it in the Christmas episode at the hospital. I don't know which kid believed...
 * Have I Got News for You, covering a somehow uniquely depressing Christmas story, about a "Lapland forest" attraction for children that was so sordid and cheap and grimy that parents starting attacking the performers and demanding their money back.

Paul Merton: Yeah. He won't be able to deliver any presents this year, because he's recovering in hospital...

Andy: He is okay, and he definitely exists, by the way.

Paul: Definitely exists.

Andy: Yeah.

David Mitchell: Otherwise, how could he have had the shit kicked out of him?"


 * The Fresh Prince of Bel Air. Simultaneously inverted when it has to be explained to Will that Shaft was never a real person.

Magazines

 * The famous newspaper response, "Yes, Virginia, there is a Santa Claus."
 * It should be noted that that newspaper response did not verify Santa as a living, breathing creature with a red suit and reindeer that goes "Ho Ho Ho". Rather, that his spirit of goodness and generosity embodies the people of Earth around Christmastime every year. Read for yourself.
 * The article, a man telling a young girl, in the sweetest way, that there is indeed a Santa Clause when other adults would just have thrown such a foolish letter away because it's not a matter for a newspaper to answer, is a Crowning Moment of Heartwarming and a Tear Jerker. The article made this troper remember what Christmas really was.
 * Spoofed in Just Shoot Me: "Yes, Maya, there is a J. Crew!"
 * Spoofed by alt.horror.cthulhu: "Yes Virginia, there is a Great Cthulu!" (link)
 * The Straight Dope takes on the question here.
 * See also Crowning Moment of Heartwarming.

Newspaper Comics

 * Pogo reverses this at one point. A bear is dressed as Santa Claus just as the cast start discovering that there's a Georgia in the (then) Soviet Union. Afraid that the Russians stole a state, the bear reveals he's from Virginia, leading to 'Yes, Santa Claus, there is a Virginia!'.

Video Games

 * A very sick version appears in Road Kill. On the radio, a shock jock is talking about the time that he got a scatter gun for Christmas... and describes, in detail, how he used it to kill a "hobo" in a red suit with a bunch of deer who was trying to break into his home through his chimney, thus "saving Christmas".

Web Original

 * Done in a very unusual manner in the SCP Foundation. One of the SCPs is a little girl with the power to bend reality. Someone tells her about Santa, and then someone else tells her that Santa isn't real. As a result, there's now someone running around with all Santa's powers, and the Foundation can't catch him because he's 'magic'.

Western Animation
"Mrs. Claus: Poor child, he still believes in Bigfoot."
 * Interestingly, in Yes, Virginia, a CBS Christmas Special specifically about the original New York Sun editorial, this is averted; the jolly elf never appears. However, the rest of the trope is accorded with. The two characters who express overt disbelief are rude and pretentious about it, one being the Alpha Bitch and the other a Grumpy Bear . The story as a whole is clearly pro-belief; the town even has a "Belief-O-Meter", and uplifting orchestral swells correlate with this meter rising.
 * However, it is revealed at the end that the whole story has been narrated by Santa Claus (Jim Backus).
 * Recess, "Yes Mikey, Santa Claus Does Shave" - Mikey is the only one of the gang who still believes in Santa.
 * The Jimmy Neutron Christmas episode has Jimmy trying to convince his friends that Santa isn't real, going so far as to take a trip to the North Pole... where even after arriving at Santa's workshop, he's convinced it's somehow all fake. After accidentally zapping Santa and being told Christmas has to be called off, he offers to deliver all the toys from his rocket, claiming that if a mere mortal can succeed in delivering all the toys in one night, it's proof that Santa doesn't exist. Naturally, he fails, and Santa, who has gotten better, steps in at the last moment to finish the job.
 * Rankin-Bass' 'Twas the Night Before Christmas, where the nonbeliever is told with a straight face that he ruined an entire town's Christmas for having an opinion.
 * Well, he did write a nasty letter to Santa Claus as a joke in a way that made it sound like it came from the whole town ...
 * He genuinely believed what he wrote (which should make the rest of it moot), and misworded the letter unintentionally. Santa couldn't tell who really did it? He's Santa!
 * A talking mouse found Santa just too unrealistic. Yup...
 * Another Rankin-Bass example has a little boy named Iggy who vocally states his disbelief in Santa Claus in front of the disguised big guy himself. Cue this song number and Iggy's disbelief being shaken and thoroughly removed upon seeing "Mr. Klaus" flying away on his reindeer's back.
 * Danny Phantom has this trope between Jack (who believes), and Maddie (who doesn't). Their bickering over Santa around Christmas, got to the stage where it actually made Danny hate Christmas.
 * A segment of Mickey's Once Upon a Christmas. Naturally Goofy is an adamant believer, while bully neighbor Pete not only denies the existence of Santa, but also installs doubt into Goofy's son Max. In a reversal of the usual situation it's the child Max who gives up hope while Goofy the father continues to try and convince his son otherwise. Naturally, Santa is real, Max becomes a believer, Goofy proves that somehow he is always right in these situations, and Pete gets his.
 * The obligatory Christmas episode of SpongeBob SquarePants. Though Christmas is a fairly new holiday in Bikini Bottom, everyone is certain of Santa's existence, especially Spongebob...everyone except (you guessed it) Squidward. Santa of course turns out to be real...and he's scary cheerful.
 * Class of 3000 Kam argues that Santa simply cannot exsist, but it turns our he does! and gives Kam a lifetime membership to the Bigfoot Watchers Society.


 * In Santabear's High Flying Adventure, Santa sends Santabear to deliver presents to the South Pole, where people have trouble believing in Christmas, let alone Santa. Santabear's mission is slightly thwarted by Bully Bear, who wants revenge on Santa for an earlier slight, and plans to deliver broken presents to completely squash out any belief in Santa.
 * This is Candace's plot point for all of 3 seconds in the Phineas and Ferb Christmas Episode before the elves show up.
 * One episode of Dexters Laboratory had Dexter claim that Santa and his reindeer were his parents in disguise. He retains this opinion throughout the entire episode, even after we see that Santa doesn't have the same body dimensions as his dad and he mistakes an actual reindeer for his mother. This results in him shooting Santa's sleigh down, blowing up probably all of the presents that Santa Claus was carrying that night. In short, he ruined Christmas for the whole world.
 * In one episode of Earthworm Jim, Jolly St. Nick reveals he used to be a Norse god of justice (Itself a Mythology Gag) and saves the day, to which Jim comments, "Yes, Virginia, there is a Santa Claus- and he kicks butt!"
 * Parodied in the South Park episode "Crack Baby Athletic Association". Only instead of Santa, it's Guns N' Roses' Slash.
 * Grandma Got Run Over By a Reindeer: In an subversion, the reveal of Santa Claus is not the climax or the main plot point. In fact, Santa seems so casual about revealing his existence that you'd have to wonder if he was even trying to keep it secret in the first place.
 * The plot of the Fosters Home for Imaginary Friends Christmas episode, "A Lost Claus". After seeing a bunch of imaginary Santas, Mac and Bloo try to prove to themselves that Santa Claus exists.

Real Life

 * Some parents are so determined to instill belief in Santa Claus in their children and preserve that belief that they'll not only tell their children that he exists, but they'll do certain things to "prove" this to them. For example, they'll leave cookies for him and eat them, write a thank-you note supposedly from Santa, look at their childrens' letters to Santa and get the specific things on the list they asked for. And if their children show signs of wavering in this belief, they'll (in some cases) up the ante on this.
 * Norad tracks Santa.
 * St. Nicholas the Wonderworker was perfectly real.