They are calling for policies to improve air quality in urban areas.
Satellite imagery used to assess pollution levels around the world found that South Asian countries accounted for 12.2 million of the total number of affected children but that there is also a growing problem in African cities.
The study, in the Lancet medical journal, warned breathing in pollution from diesel cars is particularly risky. "Protecting children from air pollution not only benefits children".
Any cardiovascular benefits of strolling along one of London's most famous roads are cancelled out by exposure to air pollution for the over 60s, according to new research funded by the British Heart Foundation (BHF). The East Asia and Pacific region is home to some 4.3 million babies living in areas that exceed six times the limit.
Some pollution particles, such as ultrafine magnetite, can enter the body through the olfactory nerve and the gut, and, due to their magnetic charge, create oxidative stress - which is known to cause neurodegenerative diseases.
Brain development in the first 1,000 days of a child's life is critical for their learning, growth and for them "being able to do everything that they want and aspire to in life", he said.
A young child's brain is especially vulnerable because it can be damaged by a smaller dosage of toxic chemicals, compared to an adult's brain.
"Our findings indicate that in traffic congested streets, like London's Oxford Street, the health benefits of walking do not always outweigh the risk from traffic pollution", said senior author Professor Fan Chung, from the National Heart & Lung Institute at Imperial College London.
The crisis saw large swathes of north India and parts of neighbouring Pakistan blanketed in acrid air - an annual phenomenon as cooler air traps particles near the ground, cause pollution levels to spike.
Delhi closed schools in early November after doctors declared a public health emergency, but quickly reopened them - provoking anger from parents who accused authorities of "playing with children's health". This includes the prevention and treatment of pneumonia, as well as the promotion of exclusive breastfeeding and good nutrition.
It called for a greater use of masks, air filtration systems and for children to avoid travelling when pollution levels are at their highest.
"The research does convince me, though, that poor air quality does play an important role in the short-term benefit one can get from taking a walk".
The link between air pollution and respiratory diseases is well-established, but the United Nations Children's Fund, in a report on Tuesday, said there is a growing body of scientific research which shows that air pollution can permanently damage a child's brain.