latchkey child vs schoolchild

latchkey child and schoolchild both are nouns.

Word	Noun	Adjective	Verb	Adverb
latchkey child	Yes	No	No	No
schoolchild	Yes	No	No	No

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

latchkey child: a school-age child who is home without adult supervision for part of the day (especially after school until a parent returns home from work)
schoolchild: a young person attending school (up through senior high school)

Other hypernyms of latchkey child include pupil, school-age child.

latchkey child (noun)	schoolchild (noun)
a school-age child who is home without adult supervision for part of the day (especially after school until a parent returns home from work)	a young person attending school (up through senior high school)