Hi, Denise!
Congratulations on your 2012 cruise aboard the Disney Magic sailing out of New York City -- what a great way to spend the weekend!
All Disney Cruise Line (DCL) guests are responsible for obtaining proper documentation to board the ship, and
U.S. passport requirements continue to change. Therefore, DCL strongly encourages guests of all ages to have a valid passport for all cruises. Having a passport allows you to always be prepared to travel wherever you wish and offers an added measure of security when you're traveling.
With that said, you currently can provide a certified US birth certificate (and proper photo ID, for adults) for every US citizen in your traveling party since your travel does not include foreign ports of call or travel outside the Western Hemisphere.
I can tell you from experience that when our family traveled in the islands with just our birth certificates, it made me nervous about losing them as well as what we would do if someone got ill or injured while at a foreign port. I made the plunge last year and went to the trouble of obtaining US passports for all four of my children. I'm so glad that I did. It truly is worth the peace of mind.
I hope that helps you plan. Have a wonderful day and a magical vacation. Bon voyage!
Andi