This happened around 9:30 p.m. in a neighborhood near 75th Avenue and Broadway.
Tolleson and Phoenix Fire Departments were called to the scene after the man riding the tractor became trapped inside it.
When fire crews arrived, they found the full-size tractor had somehow collided with the car, leaving the man pinned under it.
Crews were eventually able to free the 30-year-old man and he was transported to an area hospital in extremely critical condition.
The two children, ages 7 and 9, were also taken to an area trauma center.
Investigators say the driver and passenger in the other vehicle were not hurt and refused treatment.
Phoenix police and the Maricopa County Sheriff's Office are trying to figure out what caused the crash.
No names have been released in this case.