I must admit to having smacked all 5 of mine on occasions when they`ve gone too far, but didn`t enjoy having to do it. Back in the 70s we were living temporarily in a small touring caravan, us, 5 kids and a cat, and one morning, child number 4, son number 1, nearly 8 at the time, was jumping up and down on the bench seat under the window, wouldn`t sit down and eat his breakfast, so after telling him several times, I knocked his legs from under him, with the idea that he`d end up sitting down. Instead, he twisted round as he fell, banging his eye on the metal window catch, it swelled up something rotten, and after they`d all gone to school, I spent all day waiting for social services to call, so sure was I that the school would have reported it!
I once intervened in an argument between my 4 year old daughter and another little girl of the same age, she was pulling my daughter`s hair out in chunks! I slapped her leg, and told her to go home and tell her mum why I`d done it, never heard any more about it.