This is the only feature animation that MGM ever produced. It was directed by Chuck Jones, and derives from a book by Norton Juster. There is no DVD of the movie yet, so I’ve put a link to the book. I haven’t read the book, so this is exclusively about the movie.
The story, such as it is, focuses on Milo, a young boy who is bored with school, and generally bored with life. He is talking on the phone to one of his friends when a large box containing a toolbooth appears in his bedroom. The toolbooth, which can talk, persuades him to drive through it, in a car that it provides. He enters a cartoon land, and picks The Castle in the Air as his destination. In the process he passes through the Doldrums, goes to the Kingdom of Dictionopolis, where he learns that the princesses Rhyme and Reason have been punished. He then encounters the Mathemagician, the king of Digitopolis, and persuades him to consent to the rescue of the princesses.
So the movie is fairly didactic, but note that it involves elements that we’ve seen elsewhere. It has the personification of qualities that is present in allegories such as The Romance of the Rose, and the didactic purpose of The Faerie Queen, so it touches the fringes of classic literature.
The movie was a flop at the box office, possibly because of its overtly didactic, allegorical content. Where it is fairly plain that Aslan=Christ, the didacticism of the Narnia books is nowhere near as obvious as it is in The Phantom Toolbooth. I think the didacticism makes it more enjoyable for adults than it is for children. It is so didactic that there is a guide on using the book in the classroom. Any book that is beloved by schoolmarms, and that won’t charm a child on its own should be avoided. Whether the book or the movie will charm your child is something that only you can judge.