The girl and her brother, who received minor injuries in the crash, were both in their pajamas, said Sgt. Steve Martos.
The children's mother had put them to bed and then couldn't find them in their home a half-hour later, Martos said.
The frantic mother went door-to-door in the neighborhood and called police to report her children may have been kidnapped. Meanwhile, the accident had occurred a short distance away.
"It's just an unfortunate tragedy," Martos said.
He said police had received calls about children driving a vehicle and the possible kidnapping.
Officers spotted the vehicle, but when they tried to pull it over, the driver veered to the right and collided with a pole, Martos said.
The mother ran to the scene "and was here when we discovered that it was her two children that were involved in this collision," Martos said.