Moms/dads, what would you do if someone did this to your child?

Thats a hard one, I had a boy hit my son one time at a play place, and I really wanted to say something to the child's mother, but then I started thinking, if she parents like that then she's probably also one to blow a gasket if I say anything to her, which would probably lead to an inappropriate scene in a child area, not by me, but probably by her. I did the same thing, just walked away, as much as I wanted to say something I didn't because of where we were. But I did have a talk with my son on how that little boy was wrong to him him like that, I figured I might as well take it as a chance to teach my son right from wrong. That mother will get her payback someday!