Even myself a n adult, if wearing a skirt or dress I wear cycling shorts underneath
Doesn't even have to be cycling shorts. They can be a bit clingy in hot weather.
There are loads and loads upon loads of nice soft cami knickers on sale from websites manifold. You don't have to wear them over knickers. They 'are' knickers. They've been available since the year dot. I've worn them with short skirts, long dresses, and even under trousers. They are just ordinary soft cotton knickers with a bit of leg. Has nobody here heard of cami-knickers?
I'm over 60, so maybe nobody has!
They are the equivalent of men's comfortable underwear. Men have had them since year dot. Women seem to think they have to wear teeny tiny bits of cloth, and even encourage their daughters to do the same. It's very sexist to buy your sons proper supportive underwear that covers his genitalia, and not do the same for your daughters. Why do parents think that's ok?
Why would you send your son to school in substantial cotton underwear which resemble shorts, yet your daughters in knickers with floppy crotches?
As a TA, I see all the boys in assembly cross legged and alert and unremarkable.
I have never seen one willy, or anything even close to it.
However, I have seen plenty of female genitalia, labia, from front row girls who have inadequate underwear. It really doesn't happen with boys.
I think maybe boys are more aware of personal privacy.