It's 'yes sir' or 'yes ma'am' with our kids. I think it is mainly a Southern thing, although I was raised here that way, but my Mom was Southern. And if we hear people tell them, "oh, you don't have to call me sir/ma'am" we say "oh, yes they do". And we do get compliments a lot about how polite our kids are. So it pays off. I even say yes sir or yes ma'am at a fast food drive through