There are two components to my answer. The easy one first — I absolutely do not believe in blanket bans on books that are “too old” or “too young” for a certain age group. Kids should have the opportunity to read what they want.
The second one is in regards to my own hypothetical children, or even my kid brother who is twelve these days, which is astounding. As I’ve mentioned before, I take a lot of care in picking out books for William, largely because I want him to like what I get him and thus like reading. Which he seems to, so excellent. He’s not the best reader, and reads a lot of things I would have been well past at his age, so I try to strike a balance between things that are written for kids his age and things that he is capable of reading without giving up on. I won’t buy him the little-kid books he loves because I think he can do better, but I do try to find similar stories in a higher reading level.
On the opposite side, you can take my reading habits as a kid — I started reading The Baby-sitter’s Club books in kindergarten and was reading Sweet Valley University when I was ten or eleven. I bring up this latter because I distinctly recall asking my mother what condoms were after reading about them in an SVU book, because from the context I thought they might be snack food and maybe we could get some. Yeah. Gross. I am certainly glad that my parents never kept me from reading whatever the heck I wanted, because I read a lot of great books that way, but I know that my hypothetical children will not be getting books with sex in them for Christmas when they’re eleven. And if they’re reading them on their own, they will be informed that I expect to be able to a) read that book and b) discuss it with them after they read it. It’s not that I want to keep my kids from reading things that are above their age-appropriateness; I just want to make sure they understand what they’re reading, because that’s really the important part.
My poor, poor, hypothetical children.