Ahoy Julie!
You can travel with a passport, passport card (which is less expensive), or your original U.S. birth certificate with the raised seal. If you plan on using your birth certificate, anyone over the age of 18 will also need to show a government issued photo ID such as a Driver License. Here are Disney Cruise Line's
travel documentation guidelines. You can use the same documents when you check in at the cruise terminal and when you go through U.S. Customs when you disembark.
Getting off the ship at ports during your sailing is different. You MUST have your Key to the World card with you when you leave the ship and when you return. The card is "swiped", making your status "disembarked" until you return and "swipe" your card again. It's the cruise line's way of keeping track of all of their Guests. When you card gets swiped, your picture will be on the computer. The crew members check you against that photo. I do always carry my Driver License with me for further identification.
I hope this helps. Please let me know if I can answer anything else for you. Thanks for visiting the Moms Panel. Bon voyage!
Have a wonderful trip Andrea, and thanks for visiting the Moms Panel