Yosher is correct. "Kid" is a demeaning term. For the most part, when you call someone a kid, during an argument at least, you are trying to establish dominance over them. It is the same thing as when people in the south called black men "boy." This is why "man" developed as a term that you call your friends, because it is the opposite of boy.
So again, calling someone "kid" implies that you are somehow better/(more mature) than them.
