The incident happened outside of a Dollar General Store in Casselberry Sunday afternoon, WESH-TV, Orlando, Fla., reported.
Police said the child's mother, Crystal Martin, 28, left her daughter in the car, unlocked with the engine running, when she went into the store.
The suspect, a man in his 20s who has mental issues because of a head injury, climbed into the car and drove off, police said. The mother saw this happen and ran out of the store to try unsuccessfully to stop it.
The suspect, whose name was not reported, drove the car to the Orlando Kia North dealership where an employee noticed the man's strange behavior and called police.
When police arrived they found the man and child unharmed.
The car and child were returned to Martin, who was issued a traffic citation for leaving her daughter unattended in the car.
The suspect was committed to a hospital under the Florida Mental Health Act.