I'm from a 'wait till you're married' house. I'm sure they assume what really is going on but secretly hope it's not happening. Denial has always been a favorite location for them. I started telling my mom about a make out session I had with a fella the other evening and she was like "Ok that's enough talking about him" and it was just KISSING.
I know they are still carrying on the same idea with my younger sisters, teaching them nothing about safe sex, so I like to make sure they know they can talk to thier big sis about everything and anything.