I don't have any kids. I have a dog though, and occasionally he acts like a child. He does naughty things and every once in awhile I'm tempted to swat his ass with a roll of newspaper. But I don't do it. I've never hit my dog thus far. Yell at him, yes. Hit him, no. I believe hitting and paddling accomplish NOTHING.
Back when I was a child, it was a common custom to hit children, and I got my fair share of swattings. My mother used to wash my mouth out with soap too if I was caught lying or saying a swear word. When I was around 10, they developed liquid hand soap and my mother used that on me. She'd rub the roof of my mouth with the soap so I couldn't get it out. That was a strange custom wasn't it? And it didn't work either. I still swear like a drunken sailor.
As long as a child KNOWS his or her parent is truly displeased with him or her, he or she will remember this. A child naturally wants to please his or her parents. The show of displeasure is sufficient punishment in my opinion.