latchkey child n 1: 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)
latchkey child \latch"key` child\, n. 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}. [PJC]