Hello, Celeste!
This is a great question!
The Pirates League is a great addition in Magic Kingdom's Adventureland, where the entire family can be made over into a variety of pirates and pirate-related characters (there's even a mermaid makeover!) for an additional fee. There's a great little video from the Moms Panel which gives you a little insight into
The Pirates League. Click on "Videos" on the right side of the home page, then click on "Moms on Planning." Scroll down and you'll see the video entitled "Pirates League." You'll have a much better understanding of the process after watching it! There's also an unofficial blogger review at one of my favorite unofficial Disney sites, allears.net. Just enter the search term "Pirates League" to find various reviews and posts.
Now, not too far away is Captain Jack Sparrow's Pirate Tutorial, which is a fun-filled pirate tutorial available to all Guests. This is located right across the walkway from The Pirates of the Caribbean attraction. Be sure to check the Times Guide when you enter the park so that you'll have a listing of the various times this is offered each day.
Have a wonderful time with your little swashbucklers in Magic Kingdom Park! Send more questions as you think of them, too; I'd love to help!