Earlier in the day, a group of children found a toy-like device in Ponba Ghalmen area of Firoz Koah city, the capital of Ghor province, and began playing with it.
But the device suddenly exploded, killing the child on the spot and injuring two others, provincial administration spokesman Mawlawi Abdul Wahid Hamas said.
The injured children have been taken to a nearby hospital for medical treatment, Hamas added.
A similar blast claimed the lives of three children and injured another in Afghanistan's eastern Wardak province two weeks ago.
(With UNI inputs)