My youngest nephew had a phase like this until he punched his favourite uncle and his uncle "punched" him back.

Not hard, and more of a touch and a push but it shocked his 4 year old self enough that he stopped punching people as he understood that if you dish it out, you better be able to take it.

Did not stop him from breaking my foot one day when we were wresting around and he did a flying heel drop to the top of my foot while I was dealing with his tag team partners (brother and cousin) who had not tagged in and were double teaming me.

It was a seriously impressive move... he had a good teacher.