Addison Hall died, and her pregnant mother and young sister were injured when the car crashed through the store's entryway.
Danah McKinnon Bozek was rushed to hospital and underwent an emergency caesarean section. Her condition was upgraded to fair on Sunday. Police say her newborn daughter, along with the woman's three-year-old daughter, Miah Bozek, remain in critical condition.
"The mechanics of the vehicle are very important to analyze and we do that with any major collision where serious injury or fatality occurs," Sgt. Amanda Pfeffer of the London Police Service told CBC News. "We absolutely have to ensure that the vehicle was mechanically fit at the time of the collision, and that will be one of the focuses of our investigation."
The collision caused panic among shoppers in the busy store on Wellington Road South. Two other people who were injured, as well the driver of the car, have been released from hospital.
On Sunday, shopper Larry Hagan stopped by the makeshift memorial of flowers and stuffed toys that has formed at the store's entrance.
"It's something that no one could ever predict," he told CBC News. "It's one of those things that's so flukey. I don't know if we'll ever find out whether it was a mechanical problem with her car, or whether it was some medical problem she had or whatever."
Police have confirmed that the driver involved in the collision was a woman in her early to mid-60s.
"She has been released from the hospital and she's absolutely an integral part of this investigation," Pfeffer said.
Store-goers traumatized, sergeant says
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.
Pfeffer said many people at the store at the time of Friday's crash were left grief-stricken and traumatized.
"This is a collision that impacted many people, including emergency responders," she said. "Those available at the scene to render assistance and those at the scene that observed what transpired. Obviously any time a child is injured in such a serious way and you witness it, you will be absolutely impacted by that."