This question may seem a little strange, but I guess it does nonetheless have to do with parenting, or with how to relate with other parents and their children.
Last evening my girlfriend and me were in a club where there was an air hockey table. We wanted to play a round and started to get noticed by a curious little girl, who was the daughter of a couple who also was there. They didn't watch her closely (but hey, who could 100% of the time?). At some point she touched the surface where the disk bounces, and I told her not to do it again, because it was dangerous for her fingers.
I was stupid enough to not warn her that the disk may "jump", and guess what happens? In a perfectly fine match (disk never ever jumped away from the field), one time the disk flies into her eye.
Of course, it was not done on purpose, and I immediately felt bad about it. Neither me nor my girlfriend felt able to comfort the girl (it felt out of place for us to do it) and we called their parents to do it. We apologized too. The guy was absolutely friendly and basically said "things happen", while the mother took care of the little girl. After a while, I saw the child smile again and noticed she didn't have any "damage". I went to her and apologized to her too, explaining that we didn't do it on purpose, and asking if she was well now. I also shook her hand and presented myself and my girlfriend.
The mother was ice-cold.
How do I handle these kinds of situations, and avoid parents' rage? Was our behavior ok with the kid? Should we have comforted her right after the fact happened?