Toronto Police responded to the scene of the fire (in the Kingston Road and Galloway Road area) at about 6 a.m.
Police said the woman and her daughter were taken to hospital in serious condition, while the father and two other children were taken to hospital with non-life-threatening injuries.
Toronto Community Housing says the survivors who were seriously injured are "fighting for their lives."
The home was reportedly engulfed in flames when fire crews arrived, but the housing authority says it appears smoke detectors in the home were working.
The Ontario fire marshal is investigating and Victim Services Toronto staff are available for those affected by the fire, while counsellors are also available to the first responders involved.