Do girls wear bras under their ballet leotards?
My DD wears undies with her gymnastics leotard. Since she hates being bunchy, we buy the special underwear for gymnastics at https://rg-leotard.com/rhythmic_gymnastics/leotards/underwear . Leotards are not like swimwear, they do need underwear.
Generally professional dancers that perform in companies such as the Russian Ballet Company, American Ballet Theatre, etc have to be physically a certain body shape, such as flat busted, small waisted, similar to that of a young boys body. Many large busted women still do ballet though. Depending on the type of leotard they are sometimes able to get away with wearing an ordinary sports bra found in normal clothing shops. Other bras are available such as special dancing bras that are low cut at the back so they can’t be seen if wearing a low cut leotard. Some bras also have clear straps which many dancers who need the support wear. Other times dancers wear body suits, which is a skin coloured suction tight type of leotard that is worn underneath a normal leotard. And as others have pointed out, some leotards have built in bras.