Another vote for Bleuet. Have been impressed with the quality and holding up over time.

These are nice https://bleuetgirl.com/collections/shop-first-bra

We started with old navy but have moved on to yellowberry (my DD is 12 and she loves them). They are super comfy. I’d start with something cheap until you figure out what she likes and fit.

There are tons of them at Target - all cotton I believe so very breathable. They are hanging next to the packages of undees.

I ordered bras from bluet for my teen

Children's Place bralettes are basically cropped camis. That's what my daughter wore when she didn't really need a bra but wanted one for modesty.

My 9 and 11 year-old girls (both without noticeable boobs) LOVE Athleta's sports bras. My older one (5'3'/95 lbs) recently took my women's size M sports bra from Target. It was too tight around on me (34A) but fits her like an Athleta XL girls. So perhaps try women's sizes at Target too.

My older daughter has Yellowberry undies (from Target) and highly recommends them. I'm going to check into them!

Athleta

I liked YellowBerry for my DD. She is 13 and still wears them. They have some styles that are pretty accommodating as they grow

Athleta

My younger daughter is 8, so not really a tween. She wants to start wearing bras. My older daughter uses Hanna Andersson cotton bras, along with some very simple racerback, some more delicate training bras (inexpensive Nordstrom brand) and a few sets of Hanes racerback style. My younger daughter loved the Hanes racerback, but complained that they were a problem during outdoor camp activities - not breathable. Any recs for a not bulky, not supportive bralette that breathes well on a hot day?

Thank you!