Drinking among teens in public needs to become socially unacceptable. It’s dangerous, and it’s often not legal. This isn’t to say that among teens in private is ok, but in private it doesn’t have implied social consent as it does when nobody says anything at a kiddush.
This isn’t to say we should drive it underground. Addressing underground activities is a different story, one that relates more to education, parenting and trust than to public behavior.