Tiffany and Travis Lewandowski, ages 7 and 4, Joslyn BullBear, 3, and Daniel Flynn, 4, died in the Saturday morning blaze.
Marlys Robertson, 66, and foster children Hoskina BullBear, 4, Jamie Karst, 16 and Justin Flynn-Smith, 7, escaped and were treated for frostbite and smoke inhalation.
Robertson said Joslyn and Hoskina BullBear came to live with her about two years ago.
She told the Aberdeen American News that Hoskina would often take his blanket and sleep on the floor, and recent subzero temperatures prompted him to move closer to the propane heater.
Before going to bed each night, Robertson would scoot Hoksina away from the heater, but he hadn't made it that far Friday night when she went to bed, she said.
``I don't know when he scooted over,'' Robertson said. ``I woke up to hear (Justin) shouting 'Grandma, where are you? There's a fire.'''
Justin Flynn-Smith is being hailed as the hero by Robertson's family, because he woke her in time to get at least some of the children out.
Day County Sheriff Doug Nelson said Karst almost got two of the others out.
``My 16-year-old grabbed the boys and ran. Then she went back in,'' Robertson said.
When she got to the living room where Hoksina had been sleeping, Robertson said she found his blanket on the heater, burning.
Robertson said she wasn't sure what time the fire started.
``When I got up, the smoke was halfway down from the ceiling,'' she said. ``I crawled from the kitchen into the bedroom, and I couldn't breathe.''
Robertson said she came within two rooms of the other children, but could not go further.
``I figured if they were still alive, they'd be screaming and hollering,'' Robertson said.
But she heard nothing and got out as fast as she could, figuring she had to take care of the two out in the snow, she said. The temperature at the time of the fire was 16 degrees below zero.
In the aftermath, Robertson said she's been haunted by a sense of guilt.
``Those children were my responsibility. They were my responsibility,'' she said. ``I feel like I let them down.''
Robertson said she had only just received the Lewandowskis.
``I had just gotten them. I didn't even have them 24 hours,'' she said. ``I didn't have time to get to know them, or even learn their birthdays.''
It took fire crews until mid-afternoon to completely extinguish the fire, which flared up a couple of times through the morning.
Robertson said the house was not insured, and it remained unclear whether the home had working smoke detectors.
Saturday's tragedy brings to at least 11 the number of young people who have been killed by fire in their homes this winter in eastern South Dakota.
In December, three children died in a Sioux Falls fire. Four children died in a Jan. 7 fire in Wakonda.
