Sitting at dance camp with the little girl

Why is it that parents think it is totally ok to let their other children run rampant in and out of dance rooms playing with things (mats, trampolines)? I swear that for the last 3 weeks, these other children have raised havoc and the mothers sit there chatting like nothing is going on and it has gotten to the point that the owner of the studio (whom is teaching & I am paying for little girl's dance camp) has asked the boys to chill out/stop running/etc. This week, she asked me to keep an eye on them as her foster daughter is among the crowd (but is not disruptive). This burns my biscuits. Why the heck should I have to watch your boys? Why shouldn't you be getting off your butts and watching them yourselves? Ugh. Empty threats don't work. Parenting does. For God's sake...TRY IT! I understand that kids are kids. I understand that sitting at dance camp for an hour and 15 minutes really isn't their thing, but then bring stuff to keep them occupied. Keep them occupied in your eyesight and stop allowing them to act like a bunch of hooligans. For the love of all that is good and right, GET OFF YOUR BUTTS!