Pollutants inhaled by pregnant women may pass through the placenta and disturb the development of the brain of the foetus.
Seventeen million babies under the age of one are breathing toxic air, putting their brain development at risk, the United Nations children's agency has warned.
The paper outlines urgent steps to reduce the impact of air pollution on babies' growing brains, including immediate actions for parents to decrease children's exposure at home to harmful fumes produced by tobacco products, cook stoves and heating fires.
One study reports a four-point drop in IQ by the age of 5 among a sample of children exposed in utero to toxic air pollution, it said.
The World Health Organization describes air pollution as a "major environmental risk to health". Contamination above that limit could prove potentially harmful for children, with risks growing as exposure does.
The report said further research was needed to study the full impact of air pollution on children's developing brains.
Air pollution has already been linked to asthma, bronchitis, and other long-term respiratory diseases.
The report notes that breathing in particulate air pollution can damage brain tissue and undermine cognitive development - with lifelong implications and setbacks.
Satellite imagery reveals that South Asia has the largest proportion of babies under the age of one living in the worst-affected areas, with 12.2 million babies residing where outdoor air pollution exceeds six times global limits set by the World Health Organization (WHO).
"Protecting children from air pollution not only benefits children", Lake added. Brain development in the first 1,000 days of a child's life influences how they will learn, grow and become "able to do everything that they want and aspire to in life", he said.
"A lot of focus goes on making sure children have good quality education, but also important is the development of the brain itself", he added.
Satellite imagery analysed by UNICEF indicates that 12.2 million of these children live in South Asia.
The united Nations is calling on governments to intensify the fight against pollution as well as to strengthen the protection of children, including through the use of facial masks and filtration systems of the air.
The European Environment Agency has found that polluted air kills half a million EU residents per year.