Quebec provincial police say Patrick Gagnon, 37, Karine Desrochers-Gauthier, 32, and their four-year-old daughter died in Tuesday's blaze in Les Coteaux, Que.
A two-year-old boy died later in hospital, while an eight-year-old boy remains in critical condition in a Montreal hospital.
According to a regional fire official, the five people were unconscious when they were evacuated from the site.
Michel Pitre added that firefighters saw no smoke detectors in the apartment.
The cause of the fire hasn't been determined and an investigation into the blaze continues.