When I was in elementary school I would watch my High School aged aunt practice her baton in the back yard every day and envy her cute, shiny majorette costumes. I found one of her old elementary school costumes from when she first started out and tried it on one day. When she caught me, she just laughed, put makeup on me to match and when none of the adults were around, she let me wear it while she taught me to twirl her smaller batons. Eventually we got caught. No one got in trouble but I was told to leave her old costumes alone. I was the "good kid" (yeah... right.. if only they knew! <g>) so I did what I was told.
She did let me have the bloomers though and I kept them for the year it took me to outgrow them. Wore them to school a couple times a week.
The theater department at the tiny parochial High School I went to provided costumes for our productions and most of the time the base for the costumes came from the girls section of the catalogs. We had 3 boys in the theater class and 15 girls so they just bought all girls parts of the costumes except the specifically male character clothing. I quite often forgot to turn in things like tights, leotards, unitards, etc... cost my parents a fortune over those 3 years.
If my grandmother (she raised me) were still around today, I doubt she'd be surprised to see me living as a girl (or woman if necessary... adulting.. blehhh.. we hates it precious...). I suspect she knew I was Tabby long before I did.
I can relate to a lot of what you said there. After finding my sisters costumes I found all of her old leotards and would wear those too. Infact I remember color coding the days of the week and would wear that color leotard to bed to sleep in. By about age 13 my mother found my stash and threw them all out. It wasn't till I moved out on my own and found the internet that I bought my own and wore again.
Also you talked about the outfit your aunt wore for band, I can relate to that as well. Around junior high school I started seeing class mates in cheerleader uniforms. I became fascinated with those that when I got yo my junior year I joined the cheerleader team and did if for 4 seasons, fall and winter x2. Sadly I never got to find or wear a cheerleaders outfit.
Since my incontinence happened, I have tried onesies (body suits) and found them to be very similar to the old leotards and swimsuits from my past.