Perth OPP are looking for a driver of a large farm tractor that may have information on a two vehicle crash Saturday on Highway 23, between Listowel and Palmerston. 

The crash injured six children and five adults.

Investigators would like to speak to the driver of the tractor that was travelling southbound on the highway in front of a white Dodge Caravan moments before the crash took place.

Police say the crash happened when a van was making a U-turn and was struck by another van.

A 4-year-old and 5-year-old are in hospital in London with serious injuries.

Any witnesses to this crash or anyone that may have information about the events that led up to it are asked to contact police at 1-888-310-1122.