Battalion Chief Phil Sutsos said the fire started around 6:15 a.m. when the children, who are all under 8 years old, woke up in the morning before their mother and put newspapers in a gas fireplace that was left burning overnight because of the cold.
The fire got bigger and spread to the floor, where one of the children tried to snuff it out with a teddy bear, Sutsos said.
There were no working smoke detectors in the house, but the smell of smoke woke up the mother and everyone escaped, Sutsos said.
"This was what we call a 'near miss,'" Sutsos said. "There could easily have been quadruple fatalities."
The house was engulfed in flames when firefighters arrived, and the blaze was knocked down at 6:36 a.m.
The mother and a toddler had inhaled some smoke, and another child suffered a minor leg burn, Sutsos said. All four were taken to Petaluma Valley Hospital.
The fire gutted the home, which Sutsos described as a one-story, 1,500-square-foot house with two bathrooms and three bedrooms. He estimated the damage at between $200,000 and $250,000.
Sutsos said staff at the nearby Miwok Valley Elementary School at 1010 Saint Francis Drive found clothes for the children and brought them to the hospital.
"They did a great job," he said.
Firefighters from the Rancho Adobe Fire Protection District, Cal Fire, and the Wilmar and San Antonio volunteer fire departments also responded to the blaze.