kid vs youngster

kid and youngster both are nouns.

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

As nouns, kid and youngster are synonyms defined as:

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

kid (noun)	youngster (noun)
young goat	a young person of either sex
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)	youngster (verb)
be silly or tease one another
tell false information to for fun