Multiple media outlets reported that Charleston County Sheriff's Maj. John Clark said Wednesday that 30-year-old Mary P. Brown had left food cooking on the stove while she was gone.
Clark says when Brown returned home Tuesday night, the house was engulfed in flames.
Investigators have not determined how long the boys, Isiah and Isiac Brown, were left alone.
Officials think Brown went inside and got one of the boys and ran back inside to get the other child and was unable to make it out.
Charleston County Deputy Coroner Kelly Myers says all three victims died of smoke inhalation.