I hit her
I hit my daughter once. It didn’t do her any serious, long-term harm. She immediately said “You hit me! Even [her baby sister] isn’t allowed to hit! I’m telling!”
I apologised and we told her other parent together and he was Very Disappointed. It was about a year ago and she still remembers that I did hit her once, and it was very, very wrong.
I do think I might not have done it if I’d known it was illegal as well as immoral. The extra constraint might have helped me keep myself under control.