I just had the lovely bathing suit shopping trip today with my 11 year old. In the last few months, she's decided that she likes to act like she's 17, so all she wanted was bikinis. I finally found one at Sears, of all places, that we could both agree on, and we got a practical tankini/boy short combo at JCP for swim lessons and water parks.
On a similar note, they really need a section of clothing for girls ages 10-14. My DD is an early bloomer, and at 11 is already a b cup. Her body is starting to mature, but in no way should she be dressing like that at 11. She's too big for kids clothes, and way too young for juniors booty shorts! It is such a struggle to find clothes we are both satisfied with!!!