*sigh*
Shitty parents and bad situation. TLDR at bottom!
Was at a birthday party of one of my daughter's friend, it was in an indoor playground. And of course there were multiple groups of kids.
So "boy A" was older (around 7) and wouldn't listen to the staff and would often climb a slide (like climb ON the slide instead of taking the stairs). "Boy A" was told multiple times not to do that (I witness the staff telling him at least 3-4 times in a 15 minutes span). Parents were at a table on the other side of the playground and were not paying attention to any of that, so I'm guessing they never realized their boy was warned on multiple occasion.
At one point "boy A" decides to climb the slide again, so he comes running, goes through the exit and turn toward the slides, only problem this time, there was a 3yo (lets call him "boy B") coming down said slide. "Boy A" and "boy B" had no time to react and so "boy B" got "boy A" knee in the face. I witnessed it, the father of "boy B" also. "Boy B" father came running saw a bloody nose and yelled at "boy A". (he was rude but only told him he shouldn't be running up the slide and that he's better go and sit down).
"Boy B" kept crying and after a few minutes only the family went away, the father obviously angry, making a few steps towards "boy A" parents, but then turning away, then finally leaving.
15 minutes later I see the mom of "boy A" asking around who the family that left was because the father was rude to their boy ... wait, SERIOUSLY???
TLDR: Was at an indoor playground, a 7yo boy ended up hurting a 3yo boy because he wasn't listening to staff and his parents didn't seem to care, 7yo mom got offended that the father of the nose bleeding 3yo yelled at him to go sit down.