["A boy was being agressive with my son in the bounce house He was twice as large! His parent wasn't supervising!", "I hate when parents don't keep tabs on their kids, especially when they are misbehaving!  What did you do?", 'I found someone to tell. Apparently the kids has issues, but he should have been watched then!']
At least you did the right thing and didn't yell at the kid yourself.
A boy started being rude to my son in the bounce house. His parent wasn't watching at all!