The 1-year-old was unhurt and quickly reunited with her mother after the car was stolen Wednesday afternoon in Allentown.
Investigators say the girl's mother left the baby in her car seat in the air-conditioned vehicle while she unloaded groceries at home. Temperatures on Wednesday were in the 90s.
The thief dumped the car about two miles away. A man passing by heard a ringing cellphone inside the vehicle and saw the abandoned baby.
The Morning Call of Allentown reports that a diaper bag containing the mother's purse was also stolen.
The theft remains under investigation.