descendant vs child

descendant and child both are nouns.

Word	Noun	Adjective	Verb	Adverb
descendant	Yes	Yes	No	No
child	Yes	No	No	No

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

Other hyponyms of descendant include scion.

descendant (noun)	child (noun)
a person considered as descended from some ancestor	a young person of either sex
	a human offspring (son or daughter) of any age
	an immature childish person
	a member of a clan or tribe

descendant (adjective)	child (adjective)
going or coming down
proceeding by descent from an ancestor