I have a 12 yo DD (13 tomorrow ) and I only limit her on a few books.( wont say the books because don't care for a debate- fight on them here ) She is allowed to read what she wants.. She has heard worse if not more from the TV, School kids and I'm sure from Utube at times. My grandfather held the same views, He believed as long as the child is reading all is good.. My Aunt has read romance novels since she was a teen ( she's in her 50's now ). My DD doesn't really care for them .. only known her to read 1 and she didn't like it too much. But I'm a open mom with my kids and there's probably not much they don't know or we have not told them including sex, and growing up..

But that is just us..

Now on the other hand, If parents find the contents of the books a little too advance for their child it might be a good thing to have the permission slips.