Kid as young goat is from the 1200s with Extended meaning of "child" first recorded as slang 1590s, established in informal usage by 1840s. Dictionary.com defines kid as (informal) child. You would use it in direct conversation with persons you know well "Does your kid collect stamps?" although I don't see it as too informal to ask someone, "Any kids?" instead of, "Any children?"
The origin of slang GOAT (in a field) for the "greatest of all time"
In Yiddish, this word is an interjection meaning 'rubbish! nonsense!,' derived from bobke, which means 'sheep or goat dung.' The word was borrowed from the Polish noun bobki, of the same meaning.
The idiom, whatever floats your boat, could refer to the American slang, floating, meaning high or intoxicated by drugs. The term “whatever” also hints that the speaker is indifferent to the outcome or choice about to be made.
It thus appears that chevon as a term meaning "goat meat" originated at San Angelo, Texas, at the June 1922 annual convention of the National [or perhaps Texas] Sheep and Goat Raisers Association.
GOAT as an acronym for " (the) greatest of all time" (also considered as a noun) originally referred to Muhammad Ali, one of the greatest boxers of all time. The first written usage is from 1992 as G.O.A.T. Inc., the name of a company incorporated by Muhammad Ali's wife. The first written usage of GOAT to refer to someone is from 1996. However, GOAT has its roots in mid-1960's when Muhammad ...
To get someone's goat is make them annoyed or irritated. But what is the goat and why does getting it annoy them? When and where does the phrase come from? What's the first known use?