Aah I see! The masks have to be dirty 
It’s a bit strange how the shoutiest proponents of children’s welfare don’t seem to credit said children with any intelligence or common sense.
I know the teenagers I work with, we talk to them about how to use masks safely and correctly, and the vast majority listen, because they’re not dumb. We supply them with clean masks anytime they need them (whether that’s because they’ve lost theirs, or it’s damp, or their parents won’t give them one) and they know we won’t judge them.
Maybe try giving the young people in your life a bit more credit?