Two other adults tried in vain to rescue the children trapped inside the blazing building in a faded mill town along upstate New York's Hudson River.
Firefighters who raced to the house within four minutes of the call Saturday morning were repelled by intense flames that engulfed the building, burning so hot that it melted the siding off the house next door.
"Everything was just fire," said Bill Brown, first assistant chief of the Fort Edward Fire Department. "Top floor, bottom floor. I wasn't risking any of my guys' lives and putting them in danger to save someone who was probably already gone."
Five children in upstairs bedrooms and one in a downstairs bedroom died of smoke inhalation. The youngest, identified by family members as Abigail Smith, turned 1 on Thursday.
It was the worst fire in memory in the tight-knit community, about 45 miles north of Albany. In 2002, four children died in a fire here.
Five people - four adults and the 5-year-old boy - survived.
Lewis Carl Smith Sr., the father of five of the children who died, and his girlfriend, Samantha Cox, the mother of 8-year-old victim Paige Cox, were injured trying to rescue the kids, Washington County Director of Public Safety William Cook said. He did not know the nature of their injuries. Samantha Cox was in critical condition at Westchester County Medical Center.
Paige Cox's stepmother, Rhoda Cox, said the little girl with blond hair and a big smile grew her hair long every year and donated the clippings to Locks Of Love.
"She had a very huge heart," Rhoda Cox said.
Fire investigators scoured the charred wreckage Sunday for clues to a blaze. It could take investigators several days to determine what caused the fire.
They were still trying Sunday to figure out how many people lived in the house.
Cook said investigators believe the blaze started in the living room on the first floor. They do not suspect foul play.
Authorities would not release the names of the victims.
But Florence Palazzo told The Associated Press that two of her daughters, 12-year-old Hope Palazzo-Smith and 6-year-old Mackenzie Palazzo-Smith, died in the fire.
The others who died were identified as Lewis Carl Smith Jr., age 7 or 8; and Emillie Smith, 3.
"They were innocent kids," Palazzo said. "None of them deserved this."
Donna Layton, the aunt of Lewis Carl Smith Sr., said she spoke to him on the phone from the hospital.
"He could hear the kids screaming to him, 'Daddy, help me!"' Layton said. "It's got to be terrifying to see your kids and not be able to help them."
The acrid smell of charred wood hung over the house Sunday in this village of some 3,000 people. Amid the mound of rubble surrounding the house were remnants of a life: an easy chair, sodden baby's clothing, the blackened, twisted frame of a pullout sofa.
Firefighters described an intensely hot blaze that melted the siding of a neighbor's house 15 feet away. Inside, fresh lumber used to shore up the wrecked building contrasted sharply with the blackened walls.
Palazzo said her daughters loved to swim and play soccer and were involved in Girl Scouts. Hope and Mackenzie had just finished the sixth grade and kindergarten and had planned to visit their 16-year-old sister before her birthday party on Saturday.
"They were bright, very intelligent kids. Neither of them looked their age, especially Mackenzie because both of them were really tall," said Palazzo, who separated from Smith four years ago and lives in nearby Lake George.
Cook said autopsies will be performed at Albany Medical Center.
He said he didn't know if the house had working smoke detectors and said it was too early to talk about a cause.
"I'm not going to speculate," Cook said.
Among the five who escaped the fire was 5-year-old Noah Bosford. The boy was staying at the house with his father, Mark Bosford, and the father's girlfriend. The girlfriend shoved an air conditioning unit out a first-floor window and pushed Noah to safety. The boy was treated for smoke inhalation.
A single funeral will be held for all six children, Palazzo said.