The answer is simple.
Children sweat because their body’s thermoregulation system has not yet matured. Their bodies are still developing and they need to produce more sweat than adults do. That is why kids often seem to be sweating excessively even in very cold weather conditions, also during the summer months when it appears that temperatures are quite comfortable. They cannot regulate their body temperature as well as adults can, so they must work hard at maintaining a normal temperature through perspiration or dehydration (not enough fluid intake). As part of that process, children will appear to sweat more than adults due to their increased “surface area” – ie., the all-over surface area where heat can escape via evaporation from the skin. At least 80% of total body heat loss occurs through evaporation among people wearing light clothes.