Young children really struggle in the heat. Their bodies are too small to cool down by sweating, like adults. And they're wholly reliant on grown-ups to find any kind of relief, be it air conditioning or shade or a cool drink. Now, new research points to a potentially lifelong setback for little ones exposed to extreme heat, which is becoming more common due to climate change.

In a study of nearly 20,000 kids, young children who experienced hotter temperatures than usual were less likely to meet basic developmental milestones than those living in nearby, but slightly cooler areas, researchers report in the Journal of Child Psychology and Psychiatry . Children in lower-income households and urban areas were especially vulnerable.

"Early childhood is a sensitive period of development

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