Over 460 million or 75% of children in South Asia, one of the world's most densely populated regions, face risks related to extreme heat every year, according to the U.N. children's agency.
Children in this region are most affected by extreme heat than anywhere else in the world, according to the report, published on Monday.
"This means that 3 in 4 children in South Asia are already exposed to extremely high temperature compared to only 1 in 3 children (32%) globally," said a UNICEF statement.
The areas affected are those where temperatures climb above 35 degrees Celsius (95 degrees Fahrenheit) for more than 83 days a year on average.
"With the world at global boiling, the data clearly show that the lives and well-being of millions of children across South Asia are increasingly threatened by heat waves and high temperatures," said Sanjay Wijesekera, UNICEF's South Asia regional director.
The U.N. warned that children in Afghanistan, Bangladesh, India, Maldives and Pakistan are at "extremely high risk" of the impacts of climate change.
"We are particularly concerned about babies, toddlers, malnourished children and pregnant women as they are most vulnerable to heat strokes and other serious effects," he said.
Children are much more at risk from extreme weather, as their bodies are less able to cope with heat than those of adults. UNICEF cited a fast heartbeat, headaches, organ failure and fainting as consequences.
"Young children simply cannot handle the heat," added Wijesekera. "Unless we act now, these children will continue to bear the brunt of more frequent and more severe heatwaves in the coming years."
In the southern Pakistani province of Sindh, which was hit by catastrophic floods a year ago, more than 800,000 children were at risk of extreme heat in June 2023.
"For young children, ice packs, fans or misting with water can help lower their body temperature, while cold water immersion can help older children," advised UNICEF.
About 1.2 degrees Celsius of global warming since the late 1800s, driven by the burning of fossil fuels, has made heatwaves hotter, longer and more frequent, as well as intensifying other weather extremes such as storms and floods.
July was the hottest month ever recorded globally, with searing heat intensified by global warming affecting tens of millions of people in parts of Europe, Asia and North America.
Scientists say the world will need to adapt to the heat and other impacts already caused by emissions – and that carbon pollution must be slashed dramatically this decade to avoid worse in the future.
