Would you say "it's impolite" to your kids?

Would you normally say "it's impolite [any continuation or no continuation at all]" or the word impolite is too formal for kids and you would rather choose to express the same thought in a different way?

The reason I asked this question is because the other day I witnessed this scene: A mother (Asian) in a restaurant was correcting her child's behaviour saying, "Don't put your feet on the couch" when her child asked her why she was not allowing him to do so, she said, "because it's impolite." Her friend who was sitting next to her (obviously British, judging by his accent) said, "We wouldn't use the word impolite when talking to children, it's too formal."

It seems to me that I have heard some native English speakers (I don't remember whether they were Americans or British) use this word when talking to their children. On the other hand, that mother's friend didn't need to lie. So I decided to ask this question here.

Solution 1:

I think impolite is the most polite word to use when you're pointing out or warning the kids against bad etiquettes or rude manners.

Solution 2:

I'd say it. I'm not an expert, but I think kids generally get the idea of oppositeness pretty well, and since one teaches them the word "polite" pretty early, I wouldn't hesitate to teach the prefix "im—" and other not prefixes. Although it's true that you don't hear impolite often in casual speech. One fear, of course, is that they'd start appending "im—" to every other kind of word to negate it, but I've read that's how they naturally learn the rules of grammaticality, by broadly over-applying and then restricting to exclude irregular forms.

EDIT: If you're talking about register, as n0nchun apparently thinks you are, isn't that kind of a silly thing to be worried about? I don't believe anybody would really expect a child to negotiate complex social rules that are the essence of formality; in most societies, they are given many, many years, 'till at least the age of puberty 'till they are expected to reliably chose words of the appropriate formality. And mostly, the worry is that children up spoiled and improperly informal; I'd personally be delighted if my future kid was precocious in picking up appropriate formalities before his age.

Solution 3:

I just asked my mom, who was often complimented on how well-behaved and polite we three were. (I only tried to wrestle that gumball machine once, after all.) She says that you use the vocabulary with your children that you want them to use. You treat them the way you want them to treat others, and that includes speech. So, no, using words like polite and impolite is not "too formal." It's a way of instructing them to use words like "polite" and "impolite."

If I were talking to an adult, "impolite" is the word I would use, because I think it shows a certain amount of respect and intelligence. It's also the word I'd use with my three-year-old cousin because the meaning is appropriate, but it's more subtle than "rude" or "bad." If I tell him he's being bad, he gets upset. He knows what that means. He wants to be a good boy, but he's three and he doesn't know all the rules, and throwing trains at cousins is FUN. When I tell him he's being impolite, he gets serious, and calms down to avoid being "bad." He understands that "impolite" is a sort of warning while "bad" and "rude" both mean he's actually done something wrong.

Purely anecdotal evidence, I know, but those are my personal observations.

I noticed a sort-of theme in some of the answers about explaining things to children, which I agree with in principle, and my mom claims she once did as well...Until she actually tried it. She could try to explain things until she was blue in the face, and we would still just ask "Why?" And it seems to get worse the smarter a kid is. What do you say when a kid wants to know why the dirt from your shoes will get on the bench, or why there's dirt on your shoes at all? Are you really going to try and explain static electricity and all the other stuff involved (I admit, I don't actually know)...?

Personally, I have trouble explaining why my cousin's throwing his trains at me is bad. I have no problem telling him that throwing trains, or anything, at anyone, especially me, is very bad, and he should never, ever do it. Because I said so. And so does Mommy. And Daddy. Yes, I mean it...And no, throwing AT and throwing TO are completely different. NO! if you're throwing it TO me, you have to warn me!...I know it's not as much fun, but that's just how it works. Because I said so. Trust me.