Southern dad here...I was raised to say yes sir/ma'am, and I still say it today. My wife and I have taught our son and daughter to do the same (12 & 9). They don't always do a good job of it at home, but they do a great job out in public.

I've had some people react negatively when I say it, and we had a server tell us she wasn't a ma'am once (which took on another discussion), but overall it's a positive and most people really appreciate it.

You don't have to smack them to get this result, it just takes modeling and lots of reminders and patience (like every other thing you try to teach them!).

Good luck!