Firefighters were called to their condo in the 2500 block of Old Farm Road near Westheimer around 12:30 a.m.
The children and three adults were taken to the hospital and are expected to be okay.
While they were in the hospital, firefighters brought in fans to clear out the carbon monoxide and tested to make sure the gas was gone.
It's not clear who called 911 or how they figured out something was wrong.
Officials are still investigating the exact source of the carbon monoxide but think the family may have accidentally left their car running in their closed garage right below the condo.
Carbon monoxide has no smell or color, so you don't necessarily know it's in your house until the poison has spread.
Side effects of carbon monoxide exposure include feeling nauseous and queasy.
The Centers for Disease Control and Prevention recommends installing a battery-operated or battery back up CO detector in your home to help prevent poisoning.
You should also check or replace the battery when you change the time on your clocks each spring and fall. It's recommended you change your CO detector every five years.
The CDC says another way to help prevent carbon monoxide is by making sure a qualified technician services your heating system, water heater, and any other gas, oil or coal burning appliances every year.
You should also never use a generator inside your home, basement, or garage or less than 20 feet from any window, door or vent.
Click here for more tips.
RELATED: 18 people sickened by carbon monoxide at NW Harris County apartments: firefighters
SEE ALSO: Tips to protect yourself from carbon monoxide poisoning
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