According to Pennsylvania State Police, an adult woman and 11 children were riding in an open flatbed trailer that was being pulled by a tractor in Lower Chanceford Township.
The driver lost control and left the roadway, causing the trailer to flip and roll down an embankment, throwing all of the passengers out of the trailer.
According to the York County coroner, 36-year-old Katie Ann Stoltzfus, 14-year-old Mary Stoltzfus , and 7-year-old Naomi Stoltzfus all died in the accident. Stoltzfus was the mother of the two girls, who were all residents of Brogue, York County.
Caleb Fisher, a 9-year-old boy, also died in the crash.
The coroner stated all four victims died of multiple blunt force traumatic injuries.
At least other three children were flown from the scene and others were transported by ambulance to area hospitals in various medical conditions. The adult male driver was transported from the scene in serious condition.
Officials say they are not sure how the tractor lost control when it was en route to a recreational area on Friday.
The PSP Troop J Collision Analysis and Reconstruction Specialist Unit, Forensic Services Unit, and Criminal Investigation Unit responded to the scene to assist in the investigation. The York County Coroner also responded to the scene.
The accident at the Otter Creek Recreation Area closed Route 425 (Furnace Road) in both directions and there were initial requests for several medical helicopters, according to the Pennsylvania Department of Transportation.
The accident was originally reported by officials as a horse and buggy crash but was later corrected by law enforcement.