kid vs man-child

kid and man-child both are nouns.

Word	Noun	Adjective	Verb	Adverb
kid	Yes	No	Yes	No
man-child	Yes	No	No	No

As nouns, man-child is a hyponym of kid; that is, man-child is a word with a more specific, narrower meaning than kid:

Other hyponyms of kid include army brat, babe, baby, infant, female offspring, male offspring, stepchild.

kid (noun)	man-child (noun)
young goat	a child who is male
a young person of either sex
a human offspring (son or daughter) of any age
soft smooth leather from the hide of a young goat

kid (verb)	man-child (verb)
be silly or tease one another
tell false information to for fun