Welcome aboard, Andrea! You must have a vacation with Disney Cruise Line coming up soon! You didn't mention which ship you're sailing on or which itinerary you'll be enjoying, but I promise that no matter where in the world your Disney ship takes you, you are in for the most magical vacation you can imagine!
There are different Passport and Travel Documentation Requirements for different itineraries. If you are traveling to the Bahamas or Caribbean, for instance, as a U.S. citizen, a passport card will suffice as identification. If this is your itinerary, you can even skip the passports altogether and simply use your government issued photo I.D. like a driver's license along with the original or copy of your state issued birth certificate. But, my family prefers to travel with passports though, because in the unlikely event that you'd need to fly home from a foreign port of call and miss the ship due to an emergency, guests can much more easily do this with a passport. Take a look at the requirements for
Passport and Travel Documentation for the Bahamian and Caribbean Cruises with Disney to get specifics.
Some other itineraries like the European sailings require a passport, not the card, so you'll need to verify the requirements for your exact sailing.
You may want to call the agents at Disney Cruise Line at 800-951-3532 to discuss the details of your particular sailing to be sure you arrive with the correct travel documentation. Have fun planning, Andrea!