Ahoy, Kim!
Welcome to the Disney Parks Moms Panel! It sounds like you or someone you're sailing with has a love for mermaids! I grew up watching The Little Mermaid and often pretended being a mermaid while swimming with my friends. We never had mermaid tails, though! Wow!
I've never spotted a mermaid swimming in the ocean while at
Castaway Cay so I called and spoke to a Cast Member at Disney Cruise Line to see what their policies are on mermaid tails and monofins. Unfortunately, neither mermaid tails nor monofins are permitted onboard the ship or at Disney's Castaway Cay. I'm so sorry!
Although mermaid tails and monofins aren't allowed, Guests (ages 5 and up) are able to
rent snorkel gear on Castaway Cay and explore the schools of fish and sunken treasures under the sea. If your water-loving crew has their own snorkel gear at home, they may bring it along to Castaway Cay to enjoy the Snorkeling Lagoon located off Castaway Family Beach!
There is so much splashtacular fun onboard as well as on the beautiful island of Castaway Cay. I can't wait for your family to experience it all!
Beth