My Junior Bridesmaid doesn't like dresses

My stepdaughters-to-be are going to be the junior bridesmaids in our upcoming wedding. They are the sweetest girls. The eldest (who will be 11 when we get married) is a girly girl who loves wearing dresses and jewelry and flowers and makeup. The younger (who will be 10 when we get married) does not love dresses or frilly things. At first, I asked her if she'd like to wear a white t-shirt and tutu skirt combo and she seemed ok with that. The more I think about it, I'm not sure if that will be ideal for her. Did anyone have a "tomboy" junior bridesmaid or even a junior groomsman? Any leads on good attire? I was even thinking a cute floral romper or a pair of loose shorts and a tee shirt. We are getting married on the beach, so comfort and cool fabrics are ideal. Also, they are both nearly out of girls sizes and will likely be in juniors sizes when we get married next June. Thanks for your help!!! Pictures are a plus!