I once saw a man laying into a ten-year-old girl, hitting her around the head with a rolled-up newspaper. He was in an absolute rage with her.
I had no choice other than to go to the girl’s aide. I have seen mothers smack their children in shopping malls etc and accept that it is nothing more than a tap. The child reacts predictably to the sting and a change in behavior instantly occurs. How long for is the question, as you point out.
I still feel that it is the parents who need more education in the area of controlling their children.