Philadelphia police said a 7-year-old boy accidentally shot his 8-year-old sister while playing with a gun in the city's West Oak Lane section.
The shooting happened shortly after 10 a.m. on the 1900 block of Georgian Street.
Police said the boy was playing with the gun when it went off, striking the 8-year-old in the arm. She was taken to Albert Einstein Medical Center in stable condition.
It is unclear if the children were under adult supervision at the time of the incident. Police are still investigating.