Police said the truck crashed into the rear of a buggy carrying nine people about 8:30 a.m. Sunday near the central Michigan village of Sheridan.
The Daily News in Greenville reports the crash killed a 12-year-old boy, a 9-year-old girl and a 7-year-old boy who were riding in the buggy. The six other occupants were hospitalized in critical condition.
A preliminary investigation indicates the two vehicles were traveling east when the truck collided with the buggy.
The driver of the pickup was not injured, and troopers say he was cooperative following the crash.
The crash remains under investigation. Additional details, including the victims' names, haven't been released.