I think as long as they're happy you really can't be mad at anything. I think the main thing I would be concerned with wouldn't be their preference but that they are being safe. My mother wouldn't buy me birth control so I had to go out (at 16) and go to the obgyn and get it myself. And I don't think a lot of girls in their teens would do that. So I would be more concerned that they are being safe about it. I think most everyone goes through a stage of being confused about something dealing with sexuality and its best to allow them to be open about it. Making them feel guilty about it only causes problems later on down the road.