Here's why:
* Magical Elements: The story features a magical train that travels to the North Pole, which falls squarely into the fantasy genre.
* Target Audience: The book is written for children, with simple language and engaging illustrations.
* Themes: The story explores themes of belief, wonder, and the power of imagination, which are common themes in children's fantasy literature.
While the book does have some elements of adventure, the core of the story and its intended audience classify it as a children's fantasy book.