She has been identified as Addison Hall of London.
The girl's pregnant mother and three-year-old sister were also struck when the driver of a red Monte Carlo reversed through the front entrance of the store around noon on Friday.
Danah McKinnon Bozek was rushed to hospital and underwent an emergency C-section. Her condition was upgraded to fair on Sunday.
Police say the newborn, along with the woman's three-year-old daughter, Miah Bozek, remain in critical condition.
The collision caused panic among those shopping in the busy store on Wellington Road South. Two other people who were injured in the crash as well the driver
of the car have been released from hospital.
Police are asking any witnesses to come forward.
The London Free Press says the car was driven by a woman in her 60s.
Police are still trying to determine whether charges will be laid.
Bozek's husband, Steve Bozek, posted a photo of his daughter Addison as a new profile picture on his Facebook page Saturday, a day after the tragedy.
The posting has prompted an outpouring of condolences from friends and family.
Danah and Steve Bozek were married in 2012, according to her Facebook page.