I think Robert meant "pre-teen." Although, I would write it preteen, since the hypen often disappears from use--"today" used to be spelled "to-day." " Last, by definition, a teenager is someone between 13 and 19. Do you hear the word TEEN in 13, 14, 15, 16, 17, 18, 19? Oh, and a 17-year-old really is (still) a child, although he or she might not like to be called that. If someone is not acting his age, they are being childish and can be called a child. Example: John may be 45, but he still acts like a child. John is such a child. But we would not use kid in this context. Child here is demeaning. We could use kid to describe an older person. This would be used as encouragement. Let's say your sister just turned 30, or 40, or 50, or... And she thinks that she is getting so old. You could make her happy by telling her that she is just a kid. This means she is still young.

An 17-year-old is not a child. A child (and a kid) are under 10. A per-teen is 10 or 11. A teenager is 12 to 16. A young adult is 17 to 21. Child' is formal. 'Kid' is informal.

Child is used in formal and informal contexts. Kid is used only in informal contexts.

"kid" can also mean a baby goat. Jonny's answer, above is good. Some words are very informal. "Kids" is informal, but acceptable almost anytime, not VERY informal. . To me to call one child a "kid" can be almost insulting. "Get the kid." "That kid over there." . But, "kids" has no such feeling. I must go now, if I am to collect the kids from playcentre on time. This may be a local interpretation.

Children is the plural of child and kids is the plural of kid :D ( Guess I'm trying to be funny,