boy vs man-child

boy and man-child both are nouns.

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

As nouns, man-child is a hypernym of boy; that is, man-child is a word with a broader meaning than boy:

Other hypernyms of boy include male offspring.

boy (noun)	man-child (noun)
a youthful male person	a child who is male
(ethnic slur) offensive and disparaging term for Black man
a friendly informal reference to a grown man
a male human offspring