I grew up with a paradox – my family is modern orthodox and the neighborhood we lived in was modern orthodox but my school was yeshivish. Some of my best friends growing up were boys and when I was 13 one of my teachers gave us the “boys are evil” speech. I thought she was crazy and I still do.
One important thing was that we hung out at our houses, heavily supervised by our parents. No sticky situations ever arose with the boys I hung out with. We had plenty of clean, kosher fun in our own houses [assuming you consider watching TV/movies kosher, but that is a different debate for a different time]. Some things we did was play ping pong, board games, chess – we even went hiking and did outdoor stuff.
I even used to go out to “non kosher” places like the pool hall nearby. Our parents trusted us and we never did anything bad. At one point, one of my friends met a guy who wasn’t so kosher and I sat down and spoke with her parents. I felt that as her best friend, it was my responsibility to make sure that she did not go astray. Although she was upset when she asked me if I had told her parents, she did thank me later.
Its important to know your kids and help them develop into stable, solid adults. Rather than try to forbid them from so many things, help them gain the confidence to act as a true ben/bas torah in all situations.
So no, I dont have a real answer, but what worked for me was my mothers trust and the ability to hang out at home. I never had a need to go out and do anything bad, because I had plenty of good, clean fun right at home (and at my friends home).