Unlike in adults, sweat from children does not have a foul odour

                                                                         

Sweating is a natural mechanism of the body by which the temperature of the body is controlled. It allows cooling of the body by evaporation of sweat produced by the eccrine and apocrine sweat glands. Sweat evaporating from the skin cools the blood and this lowering of the blood’s temperature is used to help regulate the temperature of the other organs around the body. The human body has about four million sweat glands. About three million of these, the eccrine sweat glands, distributed all over the body, are found in great numbers over the soles of the feet, forehead, palms and cheeks.

They produce a clear, odourless fluid consisting of water and salts mainly sodium and potassium. If allowed to evaporate, it does not usually cause a bad odour or bromhidrosis.
The apocrine gland is a type of sweat gland that produces sweat that has protein and carbohydrates, this is the reason for  the formation of yellow stains on the armpit of your shirt. It also has a more thick and milky consistency, which can smell because of the bacteria that live on your skin.

Apocrine sweat is produced by adrenaline. So when you start to work out these are usually the areas that start sweating, as your body needs adrenaline to work hard.

The million apocrine glands that form the rest of the sweat glands are located in the axilla and the urogenital region. These glands produce a colourless fluid that has proteins and fats. The bacteria present in the skin, especially in the hairy flexures like the armpit, act upon the sweat of the apocrine glands breaking it down into end products with a characteristic odour.

Unlike the eccrine glands, the apocrine glands develop and function only around puberty under the influence of the sex hormones. Therefore the sweat of children is generally odourless. However, there are a few conditions when the child’s sweat may be offensive.

Sometimes children attain precocious puberty when the apocrine glands become active under the influence of the prematurely circulating sex hormones. In a rare genetic condition known as `Fish Odour Syndrome’ the lack of a particular hormone interferes with protein metabolism and results in the accumulation of trimethylamine, a compound with an offensive fishy smell, rather like Caliban, the social outcast in Shakespeare’s Tempest.

If a child’s sweat has a persistently offensive odour despite reasonable standards of personal hygiene it might be advisable to seek medical advice and further investigation.