Lake County Sheriff's deputies responded about noon to the 12700-block of West Beach Road in Beach Park for a child who had been hit by a vehicle.
An adult family member had been moving cars in the driveway, so other children could play basketball, police said. While one of the vehicles was being backed up, the boy rode his bike behind it.
Police said the family member did not see him, but felt the vehicle hit something.
She stopped, got out and found her family member under the car, police said.
RELATED: Darrell Brooks trial: More testimony expected about deadly Waukesha Christmas parade attack
Family members started CPR on the child until deputies and paramedics arrived.
The boy was taken to Vista East Medical Center in Waukegan with extremely critical injuries, but later died.
Police did not immediately identify the child or disclose how he was related to the driver.
The Lake County Sheriff's Office Technical Crash Investigations Unit remained on the scene Monday to uncover what happened.