schoolchild vs young person

schoolchild and young person both are nouns.

Word	Noun	Adjective	Verb	Adverb
schoolchild	Yes	No	No	No
young person	Yes	No	No	No

As nouns, young person is a hypernym of schoolchild; that is, young person is a word with a broader meaning than schoolchild:

schoolchild: a young person attending school (up through senior high school)
young person: a young person (especially a young man or boy)

Other hypernyms of schoolchild include spring chicken, younker, youth.

schoolchild (noun)	young person (noun)
a young person attending school (up through senior high school)	a young person (especially a young man or boy)