system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do babies, infants, and younger children lack the perceptible/common "body odors" (armpits, feet, ass) of teens and adults?

Is this just a matter of stank-producing surface area, or does puberty suddenly "turn on" the body's persistently smelly parts?

I remember being about 12-13 when my mother first bought and taught me how to apply deodorant/antiperspirant, soak my feet, etc.  I'd obviously crossed some sort of stanky-line-in-the-sand, but why was it there in the first place?

To be clear I'm not talking about odors that "stick to" the body (as you'd have when a baby soils a diaper, a kid vomits, etc), but naturally acrid odors coming from the skin/sweat itself.  Obviously humans of all ages have the *capacity* to stink, given proper circumstances.
gpt
There are 2 different types of sweat glands, eccrine sweat glands and apocrine sweat glands.
Babies are born with eccrine glands, which produce sweat that doesn't smell.
During puberty, humans get apocrine glands in some areas, which produce a different type of sweat that bacteria love to feed on, and that is what makes the smell.