OMG, for heaven's sakes, these are bandana halter tops. Quite in style in the 70s, and we all know fashions go in and out of style. And when you have a group get-together of young girls, especially tweens, it's not uncommon to go all matchy-matchy. These girls might even have made them themselves, they are quite easy to make and plenty modest for modern girls that haven't developed yet.

Buy 'em:

https://www.amazon.com/Downright-Bandanas-Bandana-Halter-Shirt/dp/B073LM2RFG

Make 'em:

https://www.joann.com/bandana-halter-top/1853865P71.html