When ambulances arrived at 5:17 p.m., firefighters had pulled two people into the front yard and two more were pulled out not long afterward, MedStar spokesman Matt Zavadsky said.
The children are a 6-month-old girl, a boy 5 or 6, and a girl about 10. After CPR was administered, they were all taken to Cook Children's Medical Center in critical condition, Zavadsky said.
The woman was taken to North Hills Hospital in North Richland Hills, also in critical condition.
Video from the KXAS/Channel 5 helicopter showed little external damage to the house.
The cause of the fire, where it started and where the victims were overcome were still under investigation Thursday night, Ross said.
Eight companies responded to the fire, including units from Haltom City, Fort Worth, North Richland Hills and Watauga.
When the first unit arrived at 5:02 p.m., Ross said, firefighters saw smoke coming from the second floor.
"The fire was put out quickly, and they did a thorough, rapid search. The victims were brought out almost as soon as the firefighters got there," Ross said.
As darkness fell, investigators could be seen coming and going from the house, which still was decorated for Christmas. The garage door was open, and inside were children's bicycles, one with training wheels.
Clothing for little girls hung on a rolling rack.
Written by Fort Worth Star-Telegram