Leotard question, underwear or no?

[Fitter]

So parents of dancers/gymnasts, do your girls where underwear under their leotards?

I ask because my DD1 (5) was told by her dance teacher not to, so she doesn't. Now she does gymnastics instead of dance and wears the same leotards but I notice most of the girls wear undies. So I am not sure if she needs to wear them or not.