no they dont but they wear hairspray on their butt to help the leotard not ride up
Some gymnasts do wear underwear. It really all depends on what is comfortable for you. I just went to gymnastics camp this past summer and almost everyone in my cabin wore underwear except me. So really it all depends on you. I was taught at my old gym not to wear underwear because if the underwear shows during a meet you get points deducted but other gymnasts just think its weird to wear a leotard without underwear so really it all just depends on you =)

some do, some don’t. I noticed that the older girls at my gym all wore undies, but the younger ones didn’t. I never did, but I also quit before I got too into puberty. You will get points off if they are showing, just like getting a deduction for picking a wedgie!

You don’t if you take ballet. You will be wearing tights anyway, but if you wear leggings then yes.