UPDATED: 4:35 p.m.
According to Captain Nicholas Deblasis, the incident happened shortly before 8 p.m., when a man in his 20s started playing with the children at a family party on North 4th Street.
"For some unknown reason, this male retrieved a handgun from his person and accidently discharged the firearm striking the 4-year-old," he detailed.
The man immediately left the home with another person, and drove away in a silver Hyundai Sonata.
Officers arrived and swiftly transported the boy to Einstein Medical Center. He is in stable condition, after being shot in the hip.
Police later announced a person turned themselves in, in connection with the shooting. No charges have been filed at this time.