I learned a fun retaliation from my sister -
When there are wee ones misbehaving and the parents refuse to do anything, just start swearing like a sailor, thus teaching the lil' darlings some new vocabulary.
This is especially easy to get away with kids who are bumping into you, and then snap, "Oh, holy ****! That ****ing hurt! ****! Ow!!! Mother****ing Jesus, Joseph and Mary!"
It's amazing how quickly the parents will steer the kids away.
Sometimes, the parents will get upset and say, "Hey! Don't swear around my children!", to which the response is, "Sorry! It's my reflexes from being kicked and shoved. I can't help it."