latchkey child

n.

1.

A child who frequently spends part of the day at home without adult supervision, especially a school child who returns home before the parent(s) return from work. Called also door-key child.

Noun

1.

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)

pupil, school-age child, schoolchild