The World Health Organization (WHO) said a quarter of all global deaths of children aged under five are caused from unhealthy or polluted environments.
This includes dirty water and air, second-hand smoke and inadequate hygiene which can lead to fatal cases of diarrhoea, malaria and pneumonia.
As many as 1.7 million children are killed annually from polluted environments.
WHO: 1.7mn killed by polluted environments
Young children are particularly vulnerable to polluted environment
WHO Director-General Margaret Chan said, "A polluted environment is a deadly one - particularly for young children. Their developing organs and immune systems, and smaller bodies and airways, make them especially vulnerable to dirty air and water."
Harmful exposure to pollutants starts in the womb
Children are exposed to harmful chemicals via food, water, air and various surrounding objects.
The WHO said harmful exposure to pollutants can begin in the womb and continue if infants are exposed to indoor and outdoor air pollution and second-hand smoke.
The risks of pneumonia during childhood is increased along with lifetime risk of asthma heart disease, stroke and cancer.
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WHO urges governments to make environments safer for children
Children living in household without safe water and sanitation, or those polluted with smoke or unclean fuels like coal or dung, are at a larger risk of suffering from pneumonia and diarrhoea.
A WHO expert on public health said pollution posed a risk, both in terms of deaths and long-term illnesses and disease rates.
She urged governments to make places safer for children.