I've found some really cute ones in the islands that we visited. Isla Margarita I had a cute young lady with some great cover ups approach me on the beach. They were $5/ea. I've also found some cute ones in St. Thomas and Jamaica. Just in case the girls want to shop while on the cruise. Have a wonderful cruise!!
I also buy my coverups on the islands. They have a variety of unique and cute items for all sizes and ages. I have purchased for myself and my 7 yo daughter. For me shopping is half the fun of being on the islands
I would also mirror what the other folks have said regarding buying them in the islands. Depending on your destinations, it is a shoppers paradise. In fact, my girlfriend and I were on the Carnical Legend last Oct., and scored in St Maarten. We got (4) cover-ups for $25. One thing to keep in mind: bargaining power works in the islands as oppsossed to the states. Hope I helped.
I bought a cotton cover-up at victoriassecret.com. They have great suits and coverups in all sizes. I don't know how old your daughters are, but I bought a small and I'm 5 foot three 120. They aren't like lingerie or anything. I always saw some comprable ones at target.
Aventura Spa Palace-04/25/04 Rccl Explorer of Seas-04/17/05 Carnival Miracle-05/07/06