If you like time travel and enjoy books for young adults, you'll love "Johnny and the Bomb." It tells the continuing story of Johnny and his friends who live in a small English town. In this one they travel back in time to World War II with some unintended but disasterous results.
I highly recommend all of Sir Terry Pratchett's books. This is one of his few not set on the Discworld. It is both humerous and about serious subjects all at once.