Nampa Police say a mother was picking up her three children at the Country Living Mobile Home Park at 571 Caldwell Boulevard just after 4 p.m.
After she put two of the children, the 11-month old and a two-year-old in the car, a third child opened a door to get in and the 11-month old fell out onto the ground, according to police.
Investigators say the mother got out of the car to get the infant, not realizing the car was still in gear.
After she picked up the infant, police say the car rolled backward and ran over both of them.
The car rolled 90 feet, with the two-year-old still inside, until it crashed into a parked car.
Police say the mother and the 11-month-old were taken to the hospital, where the infant was pronounced dead.
The mother suffered non-life threatening injuries. The other two children weren't hurt.
Police say none of the children were in car seats or wearing seatbelts. Officers say the case in under investigation, but no charges have been filed.