Over a quarter of all children's deaths under the age of five, globally, are due to the unhealthy environment in which they live. A new report issued by the World Health Organization has detailed how 1.7 million children are succumbing to environmental risks such as air pollution, second-hand smoke, and unsafe drinking water, many of which are easy factors to solve.

“A polluted environment is a deadly one – particularly for young children,” said Dr Margaret Chan, WHO Director-General, in a statement. “Their developing organs and immune systems, and smaller bodies and airways, make them especially vulnerable to dirty air and water.”

The single biggest environmental threat to children globally is one we’ve been hearing a lot about lately: Air pollution. Respiratory infections, such as pneumonia, that are attributable to breathing in dirty air, both indoors and outdoors, are estimated to kill 570,000 children under the age of five every year. That's more than any other single cause, including malaria and unsafe drinking water.

But the impacts of air pollution are not only limited to killing over half a million children. Millions of babies are born prematurely because their mothers have been inhaling pollution, while millions more will grow up with lifelong respiratory conditions such as asthma. Even more worryingly, breathing in polluted air even stunts the development of young and growing children. One study of children living in London found that by the age of nine, those being raised in the most polluted parts of the city had up to 10 percent less lung capacity than normal.

Sanitation and unsafe drinking water, something that is easily preventable, is still a major killer for children under five years old, with 361,000 thought to die each year due to diarrhoea alone. But there are more modern threats emerging. Recent advances in technology are also beginning to have a toll on the health of the youngest in the world, too.

Electronic waste, like computers and mobile phones, that is improperly recycled is already causing serious health issues. Around 18 to 45 million tonnes (20 to 50 million tons) of e-waste is generated worldwide, with much of it shipped to developing nations in East Asia. This is then crudely recycled, often by open burning or acid baths, in an attempt to remove the few materials of value. But the process releases harmful smoke – full of toxins and heavy metals – which has been linked to cancer, cardiovascular disease, and even reduced intelligence in young children.

The World Health Organization has issued a list of ways in which governments could help to improve the health of their youngest citizens, from providing schools with safe and sanitary drinking water, to incorporating parks into urban planning.