In contrast to last week’s question–What do you think of censoring books BECAUSE of their intended age? Say, books too “old” for your kids to read?
Since I didn't have kids of my own, my answer will be hypothetical. In general, I guess I believe more in recommendations than in censorship. If something is forbidden, and grown-ups fail to properly explain why, kids usually find a way anyway. These days my guess would be that what they pick up from TV and the internet probably cause more problems than book-reading, generally speaking.
If I did find my hypothetical kid in possession of a book I thought really inappropriate for him/her, I guess I'd ask where they got it from, and if they already read it or not; and try to take a discussion from there. (Sounds easy in theory, doesn't it?!)