I just wrote ”Y'all have weird kids." I went out on a limb and it was accepted.

hehe I think that's a nice euphemism for "your kids are spawn from hell"

Veldig uvanlig ;)

Barn in itself could mean either child or children (it is an irregular noun), but because of how it is used in the sentence, the singular version would require an article. "You have an unusual child" would be "Dere har et uvanlig barn" (Disclaimer: I'm not sure about the inflection of uvanlig here. I feel like it should get a T since barnet is neuter, but it somehow doesn't look right)

I would not get offended by uvanlige, actually (despite my earlier comment on "spawn from hell"), but if they said unormale I would get insulted.

Uvanlig can mean they are especially gifted and talented, unlike the regular (vanlige) kids. But if they are unlike "normal" kids (unormale = ikke normale)... I find it hard to imagine that as a neutral or kind comment.

Yes, it's a negative prefix like un- or in-. Others you may come across are a- and dis-, which should also look familiar.

As a translation it doesn't work here ("your children are unruly") but other than that; just straighten up some of the endings into barna dine er umulige or also dine barn er umulige.

It's not on the list. And after consulting my huge Norwegian-English dictionary I don't think it fits either. But I'm really not that particular about it (fnis). (There were plenty ways to use particular! That's why I like my books even more than I like online tools.)

(Here's the current list: uncommon, weird, unusual, atypical, peculiar, abnormal, strange, unordinary, extraordinary, special)

I think you mean ‘peculiar’ ;)

Yes, the indefinite plural of "et barn" is "barn". This is a pattern that most monosyllabic neuter nouns follow.