Emergency responders were called to a home located at 59 Collette Cres., near Bayfield Street and Highway 400, at about 9:15 p.m. Friday.
Four adults were taken to hospital, including a man and woman who were in critical condition.
Eight children and two other adults were in the home at the time, all of whom got out of the dwelling safely.
On Sunday, police said that investigators were still at the scene, along with the fire marshal.
A search warrant was expected to be executed at the home on Sunday afternoon.
No charges have been laid so far.
Police say they will release further information on the matter on Monday.