Metro Swim

12 is tough. Found some age appropriate ones at target and kohls.

Johnnie B shoppers-thanks for linking, the one pieces are exactly what I was looking for for my 11 yo dd. She wears a size 16 at Justice, would you buy a size 16y there? thanks.

Lands End has cute suits but usually not a huge selection. If your tween likes what they have, they have some cute ones. We always buy LE because they offer slim sizes - nothing worse than a droopy suit!