Two sisters were playing in the front yard of a house in Bishop Lane in rural Green County, when police say the 5-year-old climbed into her mother's car and then was somehow able to put the car into gear.
The car then struck the 5-year-old's younger sister.
Police are not releasing the names of the children and the family didn't want to talk about the accident.
However, the girl's uncle said the 3-year-old should recover.
Police say she is currently listed in stable but critical condition at Kosair Children's Hospital in Louisville.
No charges were filed, but police are still investigating.
The accident happened in a rural section of Green County, near the Metcalfe County line.