By Jenn Bernstein

PHILADELPHIA (CBS) – It was a very close call for a family on the 1900 block of Georgian Road in the West Oak Lane section of the city Thursday morning.

Police say a 7-year-old boy shot his 8-year-old sister in the arm, after he was able to find a key that opened a lockbox. Inside was the handgun.

Officials say the child was able to assemble it and fired one shot that hit his sister.

“For a 7-year-old to do that, that’s pretty creative, so he was playing with it for a little bit of time” said Lieutenant George McClay with Northwest Detectives. “So far from our investigation, we think it’s an accident.”

Police say the children, and two other siblings, live with their grandparents, who were both home at the time of the shooting.

Authorities say the grandparents drove the young girl to Einstein Hospital. She was later transported to CHOP and is expected to be okay.

Police also say the gun is registered to the grandfather.

A close family friend, Beverly Jackson, was on the way to the hospital Thursday afternoon, “I’ve known them for 35 years, they are a wonderful family, close knit family.”

Police are looking into the shooting, but so far they do not expect to press any kind of criminal charges.

“We feel there is no criminality involved in this, it’s a pure accident, and everyone involved with this is very upset,” said Lt. McClay.