The boys were under the age of 5, Kittitas County Fire District No. 7 spokeswoman Richelle Risdon estimated.
Their mother suffered non-life-threatening burns and was treated at a hospital, Risdon said. The names of the children and their mother were not immediately released.
Police and medics arrived within a minute of the call that came in shortly after noon and tried to enter the home but were driven back by thick smoke, Risdon said.
Scott Ferguson, police chief for Cle Elum, Roslyn and South Cle Elum, said officers from the police department, Kittitas County sheriff's Office and the Forest Service tried unsuccessfully to enter the burning house.
"Unfortunately, we were turned away by heavy toxic smoke," he told The Daily Record of Ellensburg.
"When I got there, flames were rolling out the front door, the windows, the sides, with heavy smoke," Risdon said.
Some 30 firefighters from three departments fought the blaze, she said.
Kittitas County Fire Marshal Brenda Larsen was investigating the scene Friday night.
"This has been a rough couple of days," said Risdon, noting Wednesday's death of 7-year-old Clayton Everley of nearby Roslyn. He died after a pile of sand collapsed on him at his home. The spokeswoman said the Roslyn boy was a friend of her own son.
"All of our hearts go out to the families," she said. "Our hearts are broken. Luckily we live in a small town, and we'll somehow rally to get through this."