This is where our parents are these days. Allowing children to listen to that trash.
They are free to do what they want. Besides, just about every single kid (even under 13) has heard or taken part on adult themed conversations, which are just about as explicit as any other subject that Howard Stern talks about on his radio show.
There's no escape from taboo subjects, so it's up to parents to properly inform their kids about what is right and what is wrong before they get misleaded by either their friends or the media.
If that's the way you want to raise your kids, I suggest you to home school your kids, prohibit them to listen, hear, or read pretty much every single form of media, and by the time they turn 18 send them to Bob Jones University.