Officers were called to a building near the Sherway Gardens mall around 8:30 a.m. Wednesday.
The four-month-old was found close to another man who had also been stabbed in the Etobicoke district of Toronto.
"Our officers rushed to the scene and found the baby", Hopkinson said.
Shortly after officers arrived, Hopkinson said they took a woman into custody.
Police had initially said the baby was stabbed, but force spokesman Const. David Hopkinson later clarified that the child's critical injuries were not related to stab wounds.
However, on Wednesday afternoon police said via Twitter that the baby's injuries were "not attributed to stab wounds". "There may be another emergency run to take her to hospital".
The man suffered serious injuries in the ordeal and was also taken to hospital for treatment.
No names or identifiers regarding the suspect or the victims have been provided.
Constable David Hopkinson told CBC: 'Right now, we're just trying to save these people's lives.
Knowles said he was unable to confirm the relationships of the victims and the suspect, but said "residents of the building are involved".
"The early indications were that a woman was responsible for these significant injuries".
Police remain on scene to complete an investigation.