I think it's important to talk to your kids to their level. Obviously I don't go into great detail with my 9-year-old son, but when my daughter was 15 we would have rather detailed conversations. I mean to the point that she came in and asked if someone could really go blind if they got semen in their eye. That was quite a conversation.

Oh, and what's wrong with sodomy? (I live in Kansas so the stuff my wife and do in the privacy of our bedroom breaks the state's anti-sodomy laws.)