Exposure to toxic air both indoors and out kills some 600,000 children under the age of 15 each year, the World Health Organization warned Monday.
This has tragic consequences: In 2016 alone, some 600,000 children died from acute lower respiratory infections caused by polluted air, the WHO report found.
"Polluted air is poisoning millions of children and ruining their lives," WHO chief Tedros Adhanom Ghebreyesus said in a statement.
"This is inexcusable. Every child should be able to breathe clean air so they can grow and fulfil their full potential."
According to WHO data, more than nine out of 10 people on the planet breath dangerously toxic air, causing some seven million premature deaths each year.
Air pollution is especially dangerous for children, and accounts for nearly one in 10 deaths among children under five around the globe, the report found.
WHO's study, which examined the health toll on children breathing health-hazardous levels of both outdoor and household air pollution, focused on dangerous particulate matter with a diameter of less than 2.5 micrometres (PM2.5).
These include toxins like sulfate and black carbon, which pose the greatest health risks since they can penetrate deep into the lungs or cardiovascular system.
The report found that children in poorer countries are far more at risk, with a full 98 percent of all children under five in low- and middle-income countries exposed to PM2.5 levels above WHO air quality guidelines.
That compares to 52 percent in high-income countrie, WHO said.