The State Fire Marshal's Office told WHBQ that one of the children was taking apart pieces of a basket and putting it on a propane heater. That heater exploded.
Eva Mason lost her daughter-in-law and two great-grandchildren in the fire.
"My husband said the front of the heater was blown off," she told WHBQ.
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Eva Mason and other family members got a shovel and broke out a window to try to save them. Family members tried to go inside and get Samantha and the kids, but the smoke was too thick and the fire was too much.
"Every angle that we went ... it just seems that the smoke was just coming out at us," Eva Mason said.
Investigators told WHBQ that the children made it out of the home, but they later died at a local hospital from injuries suffered in the fire.
The state fire marshal said there were working smoke detectors in the home, but the flames and smoke prevented the family from escaping.
Eva Mason said the family isn't sure what they will do next because they do not have the money to cover funeral expenses.