The best morals kids get from any book is just the capacity to empathize with other people, to care about the characters and their feelings. So you don't have to write a preachy book to do that. You just have to make it a fun book with characters they care about, and they will become better people as a result.
Louis SacharWayside school is falling down, falling down, falling down, Wayside school is falling down my fair lady. Kids go splat as they hit the ground, hit the ground, hit the ground, Kids go splat as the hit the ground my fair lady . Broken bones and blood and gore, blood and gore, blood and gore, Broken bones and blood and gore my fair lady. We don't have to go to school no more, school no more, school no more, We don't have to go to school no more my fair lady.
Louis Sachar