The second volume in the Harry Potter series, unlike some of the later ones, is not a long book and I re-read it in less than a day. It's recommended for children of age 9-11 which is probably about right, though of course younger children read it (or have it read aloud to them) and many teenagers and adults enjoy it too.
Further reading: [[Harry Potter and the Philosopher's Stone]], if you haven't already read it. [[How To Write Really Badly]] by Anne Fine is another school story with a bit of humour. [[Skellig]] is a different kind of book with a bit of magic in the lives of children.