poster child vs minor

poster child and minor both are nouns.

Word	Noun	Adjective	Verb	Adverb
poster child	Yes	No	No	No
minor	Yes	Yes	Yes	No

As nouns, minor is a hypernym of poster child; that is, minor is a word with a broader meaning than poster child:

poster child: a child afflicted by some disease or deformity whose picture is used on posters to raise money for charitable purposes
minor: a young person of either sex

Other hypernyms of poster child include child, fry, kid, nestling, nipper, shaver, small fry, tiddler, tike, tyke, youngster.

poster child (noun)	minor (noun)
a child afflicted by some disease or deformity whose picture is used on posters to raise money for charitable purposes	a young person of either sex

poster child (adjective)	minor (adjective)
	inferior in number or size or amount
	lesser in scope or effect
	not of legal age
	(of a scale or mode) having half steps between the second and third degrees, and (usually) the fifth and sixth degrees, and the seventh and eighth degrees
	of your secondary field of academic concentration or specialization
	of lesser importance or stature or rank
	of lesser seriousness or danger
	of the younger of two boys with the same family name
	relatively moderate, limited, or small
	warranting only temporal punishment

poster child (verb)	minor (verb)
	have as one's secondary field of study