Morgan Miller said the kids were outside watching a crane at work when the poisoning occurred.
The wife of Olympic gold medalist skier Bode Miller is sharing details of a health scare that landed three of their children in the emergency room.
Morgan Miller shared a video on Instagram Friday showing the couple's three youngest children receiving oxygen in hospital beds.
In the video's caption, Morgan Miller said the children, Asher, Aksel and Scarlet, were outside watching a crane remove a hot tub from the family's home two weeks ago.
The children suffered carbon monoxide poisoning, which landed them in the emergency room, where they received "high flow oxygen for over four hours," according to Morgan Miller's post.
She wrote that the kids got carbon monoxide poisoning "due to the lack of airflow in our driveway."
"It was a terrifying experience but thanking my lucky stars they are okay," Morgan Miller wrote.
Carbon monoxide is an odorless, colorless gas that can cause sudden illness and death, according to the U.S. Centers for Disease Control and Prevention.
The gas is found in fumes from items that burn fuel, including cars, trucks, small engines, furnaces, stoves, grills, fireplaces and gas ranges, according to the CDC.
While carbon monoxide poisoning is most commonly thought of occurring in places indoors -- like inside a home or inside a garage where a car is running -- it can also occur outdoors.
In all locations, common symptoms of carbon monoxide poisoning include headaches, dizziness, weakness, nausea, vomiting, chest pain and confusion, according to the CDC.
If a person experiences those symptoms, the CDC recommends calling 911 or a health care professional immediately.
People of all ages and health backgrounds are at risk for carbon monoxide poisoning, while the most at risk include infants, the elderly and people with chronic heart disease, anemia or breathing problems. Over 400 people in the U.S. die annually from carbon monoxide poisoning.
Morgan Miller's description of what happened to her own kids resonated with her followers on Instagram, many of whom thanked her for raising awareness about carbon monoxide poisoning happening outdoors.
The mom of eight shared in a comment on Instagram that she first noticed something was wrong when one of her sons complained of an upset stomach and then "started to pass out."
Morgan Miller wrote that she took her son to the emergency room, where tests came back normal.
"I wrote the nanny to check on the other kids and she said Aksel was starting to have the same symptoms," Morgan Miller wrote. "I notified the nurse and she said if there's ever more than one with the same symptoms then they check for carbon monoxide poisoning and sure enough that's what it was."
She continued, "They had us clear the house and bring everyone down to get tested and they sent the fire department up to check our home."
Morgan Miller gave birth to Asher and Aksel, who are twins, in 2019. In addition to the twins, the Millers are parents to a son and two daughters and Bode Miller's two children from previous relationships.
The Millers are also the parents of a daughter, Emmy, who died in 2018 in a drowning accident at the age of 19 months.