Doctors in Fort Worth treated seven people, including four children, for carbon monoxide poisoning after a gas leak in their home Sunday night.
Firefighters found the family in their home in the 2400 block of Capri Drive.
A family member said the heater in the home began leaking carbon monoxide after the family turned the heat on for the first time.
"Everybody just got home and stuff, and they turned on heater because it was cold," Jose Venegras said.
The family moved into the home a few months ago and did not have a CO detector, he said.
Venegras said he and his family were settling in for the evening when the children started to feel ill. He said his younger sister was lightheaded and was passing out and a cousin was unconscious.
"Everyone was starting to fall down -- my mom and my aunt," he said.
Paramedics transported three adults to the hospital with mild symptoms. The children were taken to Cooks Children Medical Center in Fort Worth.
Venegras said two of the children are about 13 or 14 years old and the youngest is 3 or 4 years old.
None of the victims were unconscious when they were taken to the hospitals, officials said. Venegras and another person inside the home at the time of the gas leak were not injured.
They are all expected to recover.
Venegras said he thinks the gas spread throughout the house because it has a central-air system.
"Yeah, we were thinking of getting everything checked out. ... We're starting to work on it. It wasn't in good condition, like the roof and everything, we just got it fixed."
Emergency crews aired out the home.
Carbon monoxide is an odorless, tasteless gas generated from the burning of fuels or usage of motorized vehicles.The Centers for Disease Control and Prevention reports CO poisoning sends thousands of people to the hospital every year.
Symptoms of CO poisoning include: headache, fatigue, shortness of breath, nausea, dizziness, mental confusion and vomiting.
If untreated, it could cause a loss of consciousness or even death. Those with symptoms are advised to seek medical attention right away.
NBC 5's Ray Villeda contributed to this report.