Lexington County Sheriff James Metts says the boy was trying to get a toy gun out of a trunk Saturday night at a home in Gaston when he picked up a real gun also in the trunk by mistake.
Deputies say the bullet went through a car, and fragments hit Juliet Lynch in the chest. She died a short time later.
Metts says the real gun belonged to the boyfriend of the boy's mother and she did not know it was in the trunk.
The sheriff says charges could be filed in the shooting. Police did not release the name of the boy, his mother or boyfriend.