Because the mother was so weak, police had to break down the front door to get everyone out.
The children are four, seven and nine years old.
"They were carrying the kids out, almost unconscious," said neighbor Lori O'Connor.
She grabbed a coat and shoes to give to her friend. She said the past couple of days the family had been complaining of feeling sick.
"Very scary. She thought they all had stomach viruses," O'Connor said.
All four were rushed to Englewood Medical Center where they were treated by Dr. Carmine Gianatiempo.
He says carbon monoxide poisoning does come on fast and does feel like the flu.
"Headache, nausea, vomiting, muscle aches," he said.
In more extreme cases, victims can't even get out of bed. The body, Gianatiempo said, is suffocating from the inside out as oxygen in the blood gets replaced by poison.
Since you can't smell it in your home and don't want your body to be a detector, make sure you have a carbon monoxide detector. They cost about $20 and they save lives.
Investigators said there were no working detectors inside the home. They had smoke detectors, but none also detected carbon monoxide.
Investigators said the leak may have come from the hot water heater in the basement.
The mother and children remained in stable condition at the hospital on Friday night. They were expected to make a full recovery.