Michigan State Police said the buggy was on Kelly Road in Algansee Township when the pickup truck rear-ended the carriage.
The crash threw all seven people out of the carriage, five of whom were children.
Two of the children died on site.
Police say a 4-year-old faces life-threatening injuries, and a 3-year-old appears to face major injuries, WWMT reports.
An adult woman reportedly suffered serious injuries as well.
The people injured in the crash were taken to a hospital.
The driver of the pickup truck was taken into custody and was allegedly intoxicated, ABC News reports.
Police have not yet released the name of the driver.