Philadelphia Fire Commissioner Lloyd Ayers says Tasha Rose was using two rear open-flame burners on her stove to warm her 6th floor apartment at the West Park Apartments in Powelton last week.
She left the unit for a short time and found flames when she returned.
Rose tried to save her two young boys, but could only find 3-year-old Tyheed.
The other, 4-year-old Tymere, was found lifeless under a bed where he'd been hiding.
Investigators believe the boys were playing in the kitchen when an object made contact with those open flames and caught fire.