The nine-year-old girl in my family was in need of underwear, so I went shopping for some. She's tall for her age, but thin, and had outgrown her size 10. I went looking for 12s.
The thing about buying girls' underwear is that it's really hard to get away from the cartoonish, silly patters that appropriately decorate underwear in size 4 or 5. Most nine-year-olds do not want to wear cartoon underwear. I was very surprised that so much of that is offered in sizes 12, 14 & even 16.
I did finally find this great value package of Hanes. They come in briefs and bikini styles, but she likes the hipsters best. There were nine in the package, mainly white with a colorful band around the top. There were a couple in solid colors and two in cute prints with dots and cupcakes. They looked appropriate for a pre-teen, not too grown-up but not silly.
She really likes these, and I'll buy them again if I can find them.