The girl, Caroline Starks, was shot at her home in rural Cumberland County and was taken to a hospital where she was pronounced dead, the Lexington Herald-Leader reported Tuesday.
Cumberland County Coroner Gary White said the children's mother was home at the time of the shooting. He identified the gun as a Crickett, "a little rifle for a kid."
White said the family did not realize a shell had been left in the rifle, which was kept in a corner of a room.
The shooting will be ruled accidental, White said.
An autopsy was scheduled for Wednesday.