Read it with them. My mother got in to it a few years back and now she helps us read aloud when we get the book. Plus you'll feel better about it. It's something we all like - 22 down to 10. Nice family time.
How old's the boy? The books get darker... I wouldn't really recommend them for anyone under nine or ten.
Bill is 11. If he decides something is too creepy, he just won't finish it. My oldest daughter, who's 14 now, started one HP book and decided it was boring.
I haven't been in a fantasy mood for several years now. Too many great mysteries, and nonfiction. Maybe someday I will be again.