The incident happened at around 3:30 p.m. at the intersection of Large and Pratt streets in Northeast Philadelphia.
Police say the girl had just exited a school bus and was attempting to cross the street behind the bus when she was struck.
Witnesses say the bus driver retracted the stop sign and pulled off, leading drivers to believe it was okay to proceed.
The striking car did stop on scene.
According to police, no charges appear imminent against the driver of the striking vehicle.
The child is critical at Saint Christopher's Hospital for Children.