The Secret of Platform 13

The Secret of Platform 13 is a children's book by Eva Ibbotson. Inside the abandoned Platform 13 in King's Cross Railway Station lies the Gump, an ancient and magical secret passage. Every nine years it opens to take those who wish to leave the world behind for the mythical island known as...The Island. The Queen gives birth to a son the year the Gump opens again and after the Prince's three nannies are overcome with homesickness, she allows them to take the Prince with them for a brief visit to our world.

What they don't count on is running into Mrs. Trottle, who desperately wants to have a baby... even if it means turning to kidnapping.

Nine years later, a young hag named Odge learns about the rescue mission being planned by the King to bring home his son, who has been raised by Mrs. Trottle as her son, Raymond. After much convincing she joins the appointed rescuers--Cornelius, Gerkintrude and Hans--in their journey to London. Their task will not be as easy as they thought however, as Raymond is not only constantly protected, but is also an extreme Royal Brat. Though they find immeasurable help from Ben, the grandson of Raymond and his mother's former nanny, and the many magical creatures in hiding, will it be enough to bring the Prince back to the Island before time runs out?

Trope examples:

 * Adaptational Villainy: Inverted in the case of the Nuckelavee, who seems to be fairly benign or at least fairly harmless . In the original folklore that the creature appears in, it is much more malicious.
 * Ambiguously Human: Many of the Island's unusual creatures, which is why they can move or travel around London without being noticed.
 * Cute Witch: Subverted in name only. Odge is a hag with powers such as making people go bald, but unlike her sisters, she's considered pretty.
 * Doting Parent: Mrs. Trottle. She's many things, but she pulls out all the stops to make Raymond happy, even if that's exactly how he became such a brat.
 * Fat Bastard: Both Raymond and his mother are examples of this.
 * Food Porn: The meal that, unfortunately, Raymond Trottle is eating when the travelers follow him around town. Given the most attention is the knickerbocker glory.
 * Gentle Giant: Hans.
 * Good Is Not Nice: The harpies and other monsters on the Island, who serve as terrifying law enforcers.
 * Granola Girl: Gertrude. Being a fey, she has an even stronger connection to nature.
 * Harping On About Harpies
 * Have I Mentioned I Am a Dwarf Today?: Melisande is a water nymph, not a mermaid. She points out her feet to prove it.
 * Mama Bear: A villainous example in Mrs. Trottle.
 * Magical Girl: Odge is the youngest of her seven sisters, all of whom are hags.
 * Mismatched Eyes: Odge has one brown eye and one blue eye.
 * Modest Royalty: The royal king and queen of the Island. Their mansion is even open to any guests who want to stay a night or two.
 * My Biological Clock Is Ticking: The main reason why Mrs. Trottle kidnaps the Prince after adoption doesn't work out.
 * Nice Guy: Ben
 * Ridiculously Cute Critter: The mistmakers!
 * Rich Bitch: Mrs. Trottle.
 * Royal Brat / Spoiled Brat: Raymond Trottle, the whole deal: tantrums, the room of broken toys, disrespect to anyone who isn't his mother, and there's nothing anyone can do about it since his parents are incredibly rich.
 * Same Sex Triplets: Lily, Rose, and Violet.
 * Scare'Em Straight: Mrs. Trottle to Raymond
 * Strange Secret Entrance: The eponymous Platform 13.
 * Theme Triplet Naming: Lily, Rose, and Violet.
 * They Have the Scent: Not said word for word, though.
 * Villainous Glutton: While out at lunch with his mother Raymond orders fried prawns, soup, roast beef, Yorkshire pudding, fries, and an ice-cream sundae. Other times when he is out he is usually seen downing more.