I think there is a limit to what parents can know even if they monitor the kids, let me use myself as an example, When I was in secondary school, I watched bf with my friends in class, how are my parent supposed to know about that?

One day I borrowed a blue film disc from my friend to watch when my parent go to work, how are they supposed to figure that out?

I could have advance to bringing girls home when they are not around if that bad stuff was really on my mind but after few times of watching the bf, I lost interest...

but you made a point, when a child is still very young, there are some habit that the parent can stop him from doing