A teacher and a cafeteria worker were also taken to hospitals after firefighters responded to Finch Elementary School shortly after 8 a.m., Atlanta fire Capt. Marian McDaniel told The Associated Press.
Firefighters were initially told that people were unconscious at the school, but none were when fire crews arrived and all of the patients were conscious and alert as they were being taken to hospitals, she said.
Video from WSB-TV showed rescue crews carrying young children strapped to gurneys with oxygen masks on their faces.
Firefighters detected high and unsafe levels of carbon monoxide near a furnace at the school, which is on the city's southwest side, McDaniel said.
Firefighters detected 1,700 parts per million of carbon monoxide, which McDaniel called a very high level of the gas.
"It was one of the highest we've seen," she said.
Other students from the school were taken to Brown Middle School for the rest of the day, and were being released to their parents, Atlanta Public Schools said in a statement.
Firefighters were ventilating the school in an attempt to reduce the amount of carbon monoxide, McDaniel said.