When it comes to air pollution, humanity has been kicking the can down the road for decades. And now, it seems the next generation is catching up with the consequences.
The findings reveal that 93 percent of all children under the age of 15 are breathing toxic, polluted air.
That's roughly 1.8 billion children under the age of 15, and 630 million children under the age of 5 whose health and development are at serious risk.
"Polluted air is poisoning millions of children and ruining their lives," said Tedros Adhanom Ghebreyesus, the director-general of WHO, in a statement.
"This is inexcusable. Every child should be able to breathe clean air so they can grow and fulfil their full potential."
The WHO report was released in advance of the very first Global Conference on Air Pollution and Health, and it describes in devastating detail the heavy toll that air pollution can have.
Air pollution can occur both outside and inside buildings and homes, and is defined by the concentration of fine particulate matter that the air holds (less than or equal to 2.5 micrometres in size).
Because children are in a key developmental stage and because they breathe more rapidly than adults and are closer to the ground, they are particularly vulnerable to these tiny particles.
And right now, many parts of the world are experiencing dangerously high levels of air pollution.
Using global air quality data and rates of respiratory tract infections in children, the WHO report found that in 2016 alone, 600,000 children under the age of 15 died from acute lower respiratory infections caused by polluted air.
The authors of the report write that air pollution places "the heaviest burden on the smallest shoulders." But children who live in less developed countries appear to be carrying most of that weight.
Among low- and middle-income countries, the report found 98 percent of all children under five are exposed to air quality below WHO guidelines.
In high-income countries, 52 percent of children under five are exposed to such levels.
Not only can air pollution cut a child's life short, it can also lead to health burdens lasting a lifetime.
Air pollution was found to affect a child's neurodevelopment, causing lower test scores as well as difficulties with mental and motor development. It was also found to increase the risk of cancer and other chronic illnesses later in life like cardiovascular disease.
"Air pollution is stunting our children's brains, affecting their health in more ways than we suspected," said Maria Neira, the director of the Department of Public Health, Environmental and Social Determinants of Health at WHO.
Although this public health crisis has been receiving more attention in recent years, the consequences for children are often overlooked. The new WHO report is a chance to fill in that gap.
"Children are society's future. But they are also its most vulnerable members," the report reads.
"The immense threat posed to their health by air pollution demands that health professionals respond with focused, urgent action."
The organisation is encouraging health professionals to come together and address the threat as a priority. But that does not mean WHO is laying all the responsibility at the feet of the medical community.
The report also urges all countries to work towards WHO's air quality guidelines by implementing policies that will reduce air pollution.
For indoor pollution, these policies include a switch to clean cooking, heating fuels and technologies. For outdoor pollution they include a reduction in fossil fuels and an increase in renewable energy sources.
"For the millions of children exposed to polluted air every day, there is little time to waste and so much to be gained," the report concludes.
The report was published by the World Health Organisation.