youngster vs child

youngster and child both are nouns.

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

As nouns, youngster and child are synonyms defined as:

Other synonyms of youngster include fry, kid, minor, nestling, nipper, shaver, small fry, tiddler, tike, tyke.

youngster (noun)	child (noun)
a young person of either sex	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