Well, in your reply below, you found your best solution. Casually work that point about laughter and screaming being two different animals into a chat if you can, tap on their door if you must. If parents don't respond or get miffed then it is a PARENTAL problem that may call for more extreme measures... Just weigh them carefully and implement them when sober two days after they occur to you, Warrior Wench... ICU in profile pic ... a force to be reckoned with!

Tell to parents to "curb their spawn." I find it works well, especially because then they know that their little angels aren't angels at all.That or offer to beat their kids until they learn how to shut up and be respectful of other people. Say you will do this for the low fee of $100 per kid and 5th session is free. They should be able to figure out how annoying the kids are from that.

Give them a 5 gallon bucket with water in it.
When they ask what it is for - smile beautifully & say
"If you stick their head in it, they will stop making that noise"
Quietly walk away. With smile still in place.

You don't. You pick them off one by one when you catch them alone. Not a great idea, but a permanent solution.