A kindergartner died after falling off a forklift that was driven by an older child while both were playing in a north Alabama warehouse, authorities said.

A statement from the Muscle Shoals Police Department said two juveniles were at a warehouse where their parents work on the TVA Reservation when they snuck away from the adults to play on Saturday.

The children — who news outlets reported were 5 and 9 years old — found a forklift, and the older child was operating it when the younger one fell off and was killed.

Police didn’t release a cause of death, but the statement said the “horrible tragedy” was an accident and the investigation was closed.

The Department of Human Resources was contacted because of what happened, it said, but no further information was released.