I don't debate that the kids know about sex. My "innocent little sister" (according to my parents) can talk pretty dirty if she wants to. And although I'm all for no sex before marriage, I know it's not going to happen because I would like it to.
What I'm saying is teach them some responsibility. And it has everything to do with the Age of Consent... the earlier they learn this stuff, the earlier they are able to deal with having sex, and it's consequences.

As for the church... I don't think God prohibits the use of contraceptives. It's just the church doing it's own interpretation.