Welcome aboard, Kenneth -
You and your buccaneers are already in that right mindset of getting yourselves your pirate gear in preparation for the
Pirates In The Caribbean party on the Disney Cruise. As with all our cruises, my family and I always bring our own pirate gear. I like checking out accessories at our local party store or even do some online shopping prior to the cruise. I've come across good deals and quite a bit more selection and sizes for everyone in our family this way. There's a good amount of Pirate costume choices for kids, you'll just need to check out what is comfortable for them. My kids really like the glow in the dark bracelets and wands too. They stand out in the crowd, and it makes it easier for me to spot them while in the midst of all the little pirates on the deck dance floor.
It sounds like you are hitting the Disney Parks prior to your cruise... If you happen to be a the Magic Kingdom, the shop by the Pirates of the Caribbean ride has a good selection. The Disney store usually has some items too. Onboard, there is quite a selection as well. So, if you don't have time to shop for any costumes prior to your cruise, you can always check out what is onboard. Make sure you check it out a day before the Pirate Party -- it gets really crowded in the shop as everyone is trying to choose their pirate gear right before the pirate deck party.
I'm sure Captain Jack Sparrow will be thrilled to see you and your little one onboard - I've had the funniest conversations with him at the onboard meet & greets, and taking pictures with him is always a treat. He is an awesome character!
Wishing you swashbuckling fun with Pirate Mickey and his friends in May!
~ Dolly