Here's a guarantee: whatever you don't talk about with them, someone else will.
I'm a little peeved at the moment because of a fairly recent news report that aired on Good Morning America called, "Safer Sex: Some Parents Allow Their Teens to Have Sex Inside Family Home". The argument in favor of this new practice is one we've heard before with other illicit activities. "I'd rather he do it here than somewhere else."
Really? You're an idiot.