I agree that parents in the yeshiva should really be the ones to speak to the principal about the matter, but people sometimes tend to gripe about it among themselves, but never take it any further than that. Or maybe they don’t care. So as chazal say, “B’makom she’ain ish……” If they are not doing it and you are really concerned about the children’s safety, then pick up the phone, ask for the principal, introduce yourself as a concerned fellow Jew, and tell them what’s on your mind!
Also, I want to clarify that I never threatened the yeshiva c”v! I always try to make sure that my attitude towards Rebbis, teachers, and the hanhalah is one of respect and appreciation, and whenever I speak to them I try to convey the sentiment that “We’re on the same side – we both want what’s best for the child/talmidim.” As far as, telling them that they would be liable if someone were hurt c”v, that is said as a statement of fact and not a veiled threat. Attacking the yeshiva or the principal will just make them defensive and wouldn’t necessarily accomplish anything. As I said above “if you speak to them in a way which shows your concern for the safety of the kids rather than angrily or in an accusatory fashion, I think they will understand where you are coming from and take appropriate action.”
Wishing you hatzlachah and a g’mar chasima tovah.