My older boys know that they can come to me or DH about everything and anything and that nothing is a taboo subject in our house.
I have been as open and honest as I can be from an early age with them even with the stuff that makes me feel a bit uncomfortable Try explaining premature ejaculation to a 10 yr old (he heard it on a radio ad)

I strongly believe that the more you know the less you need to find out. So fingers crossed they wont feel the need to experience stuff they arent ready for just because they were curious about it.

However they also know that if they do decide they want to take the next step, hopefully with someone they trust and respect, then there are condoms available no questions asked in the bathroom drawer.