The accident happened around 3:00 Sunday morning, at the intersection of North 5th and Venango streets.
Police say that the driver of a Land Rover ran a stop sign and struck a Chevrolet Malibu.
Shortly after the accident, both men inside of the Land Rover fled the scene.
A 24-year-old female driver and her two children, all inside of the Chevy Malibu, were injured in the crash.
The driver suffered a fractured arm and pelvis, and was taken to Temple University Hospital where she is in stable condition.
A 9-year-old boy, who police say was not wearing a seatbelt, suffered massive head injuries and is in critical condition. He was taken to St. Christopher's Hospital where he will undergo surgery.
A 2-year-old girl suffered minor injuries and was also taken to St. Christopher's Hospital, where she was treated and released.
The accident is still under investigation, and anyone with information is asked to call police.