That happened at a job that I used to work at. The son had lost a gift certificate for a free Turkey for Thanksgiving. He came through my cash register line. I felt very uncomfortable and had odd thoughts of him reminding me of my step-father. So I was releaved when he got out of my line.
Later, a co-worker saw him yelling at his son and called the police. I made some kind of odd comment about him having reminded me of my step-father. I had suspected that he would yell or do something worse to the son. However, I had no real reason to believe except for my odd reaction to him. He was just totally silent and seemed like he was struggling to keep his temper in check which is what I think made me react so emotionally to him.
I don't know if I could have the guts to interfere with a parent and child. Especially since I suspect that I might think something is child abuse when it isn't.