SPRING HILL, Kan. -- Four children were recovering Saturday morning after a night of family fun took a terrifying turn on Friday night.

A witness said the family was taking a tractor ride towing a trailer full of kids on South Green Road near Spring Hill, Kan., when it rolled backwards causing the passengers to be thrown from the trailer.

"It ran completely over 'em," said Greg Lancellotti, who witnessed the accident. "They were left here in the middle of the road. The tractor continued to roll on down the hill."

Officials said two adults and a child were up front in the tractor when the driver tried to change gears while going up a hill on a paved road. The tractor rolled backward and jackknifed back onto the trailer.

The injured children all were under 10 years old and were taken by ambulance to a hospital. Two of the victims were treated for minor injuries and two had moderate-to-severe injuries.