12/24/2014 10:13 EST | Updated 02/23/2015 05:59 EST

Les Coteaux fire victims ID'd as Patrick Gagnon and Karine Desrochers-Gauthier

"I had a great year! Thanks for having contributed," reads Karine Desrochers-Gauthier's final Facebook post late on Monday night.

Four hours later, a fire that started in the living room killed her, her partner Patrick Gagnon and two of their three children.

Desrochers-Gauthier, Gagnon and their four-year-old daughter, Laurie, died in an apartment fire in Les Coteaux, Que., in the early-morning hours on Tuesday.

Their two-year-old son, Felix, died later in hospital and their eight-year-old son remains in critical condition at Ste-Justine, a Montreal children's hospital.

A regional spokeswoman with Quebec's provincial police service said a smoking device is currently a hypothesis under consideration as police continue their investigation into the fire in Les Coteaux, just west of the island of Montreal.

The small and relatively contained fire started in the living room of the home of Desrochers-Gauthier and Gagnon, on the third floor of a small apartment building on Des Bouleaux Street.

Four of the five victims were found in their bedrooms by first responders; the fifth person was found in the bathroom.

Lac St-François regional fire Chief Michel Pitre said it did not appear as though the home was equipped with a smoke detector.

Neighbour Anne Pelletier's seven-year-old son is best friends with eight-year-old Mathis, the only survivor.

She said her son is praying hard for his friend.

"He's wondering where he'll go after, who will take care of him, if he'll be able to see him again. He even asked, 'Mom, will I have to take the plane to go and see Mathis?'" Pelletier said through tears.

A Facebook page has been set up in memory of the family members who died in the fire.