What is the genre of the Phantom Tollbooth?

The Phantom Tollbooth is About a Boy named Milo who is bored about life. One day Milo receives an anonymous gift: a toy tollbooth. He realizes that it actually leads to a totally different world, and it is up to Milo, a watchdog, an uppity bug, two kings who hate each other, and a boy who is four feet off the ground to rescue Rhyme and Reason--the princesses. The genre is Fantasy.