child vs man-child

child and man-child both are nouns.

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

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

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

child (noun)	man-child (noun)
a young person of either sex	a child who is male
a human offspring (son or daughter) of any age
an immature childish person
a member of a clan or tribe