The incident happened at Carolier Lane and Route 130 North in North Brunswick around 3 p.m.
Law enforcement sources say the bus hit the car, completely crushing the side of the vehicle, though it is unclear which went through the intersection illegally.
The child was rushed to the hospital in critical condition, while two other occupants in the car and the bus driver were also hurt. Authorities are investigating reports that the child was unrestrained.
There were no students on the bus.
The cause of the accident remains under investigation.