The couple were found Tuesday afternoon at a Monarch Parade property in Mitcham.
No arrests have been made and the police are not looking for anyone else involved in the incident.
Police said the woman was hospitalized for fatal injuries.
The child was pronounced dead shortly after being taken to the hospital.
Police said the relatives were informed and that a post-mortem examination would take place in due course.
Officers remain in the area and a crime scene is in place as investigations continue.