Police say the accident occurred on Kentucky 52 seven miles east of Richmond.
A Chevy four-door sedan and a Buick SUV collided. Joshua Nelson, 28, and his son Jacob Nelson, 3, were killed in the crash.
Taylor Shea Nelson, 24, and Jonah Nelson, 1, are both in critical condition and are at UK Hospital. The Nelsons are from Waco, Kentucky.
Lance Patterson, 46, and Cody Patterson, 16, were sent to Patty A. Clay Hospital. Their condition has not been released. The Pattersons are from Richmond, Kentucky.
Police say Lance Patterson was driving eastbound, and was trying to pass a vehicle in front of him and collided almost head-on with Nelson's vehicle.