Yes, we guide out kids...diet, dress, language, etc but we do that so they learn to make their own choices. Not so that we continue to control those choices.And for many of us, it's just close to impossible to monitor what our kids read.
My DD reads too fast and I don't lock my bookshelf the way gun owners lock their gun lockers or some folks lock the liquor cabinet. (I don't, BTW)
Would I have preferred my DD not read my Anais Niin collection last summer? Yes.
Did I kinda kick myself for having it on the living room bookshelf? Yes.
But it opened up a dialogue about her budding sexuality, the changing nature of what is considered sexy, etc.
I do not pre-read at all - there's no way I could. I have a pretty good idea of what's she's reading much of the time, and she's certainly read stuff I was surprised by. I try to get her to the library regularly to keep her supplies up .
I'm actually not worried about sexual content if it's mutual etc. It's violence that I worry most about. I should say that my method is based on what I experienced and what I see about my kid, and it may be/is very different for other people. I have read stuff that I would love to expunge from my brain, but it's there. Once you read it, the deed is done. I read a large range of genres, including crime fiction. I often just go ""yup, ok, jump ahead a bit because I don't need that imagery just now, thanks!" I'm not terribly faint hearted, but I definitely have certain images/themes that squick me out and I avoid.