When I was 16, my dad told me that if I have premarital sex, I would go to hell. When I had my first sexual experience at 23, my first thought was, "Wow. That would have been worth going to hell for."
I've known for many years; kids will have sex no matter what parents think about it. Its part of life. In my opinion, its best to teach them how to properly use birth control, but to hold out just a little longer for that special someone.