A 3-month-old girl was tragically killed when she was struck by a car after her mother lost hold of the baby and the car rolled backward, police said Sunday.

The baby's family was set to eat at a fast-food restaurant in the 11200 block of Fourth Street in Rancho Cucamonga, east of Los Angeles, just before noon.

The father of the child went in to place an order as the mother was helping her children get out of the car.

The family was borrowing a car, and the child's mother was unfamiliar with the operation of the vehicle, police said in a preliminary investigation.

The mother believed she had turned it off and was unloading the three-month-old from her car seat, as well as helping her three-year-old son get out.

After removing the baby from her car seat, the baby’s mother realized the car was still running, police said.

She was holding the child as she walked around to the driver’s side, police said.

The mother reached in to turn off the vehicle, and somehow the car rolled backward, police said.

She tried to apply the brakes, but lost hold of her baby, police said.

The baby fell and was struck as the car rolled backward. After stopping the car, the mother was able to rush to her daughter.

The 3-month-old was transported to the San Antonio Community hospital in Upland where she died, police said.

The mother of the child was devastated, but cooperative, so she was released from the scene.

Authorities are still investigating.