This is one of the best books for kids on the planet. The Phantom Tollbooth by Norman Juster is graded for kids aged 9 to 12, but I have found that even 5 and 6 year olds can enjoy the story if it is read to them. The video is good enough to have made my kids beg me to read them the story.
Milo is a bored kid who suddenly finds a tollbooth in his room. When he takes the accompanying car for a ride, he finds himself in a new world. The story is like Alice in Wonderland meets your third-grade teacher. Milo has to save the land, which has fallen into confusion since the Princesses of Rhyme and Reason were banished, by rescuing the princesses from the Castle in the Air. On his way, he passes through Dictionopolis, Digitopolis, and the Doldrums, among other places. He fights numerous enemies of Rhyme and Reason.
I found the Doldrums fascinating as a child, and even more so as an adult, seeing as how I find myself getting stuck in them after a hard week at work. The means of escaping the Doldrums works even in the real world.
In any case, this is a fantastic book for kids and parents alike, and I highly recommend it.