information on the Western Hemisphere Travel Initiative (WHTI):
"Closed Loop" Cruises: U.S. citizens who board a cruise ship at a port within the United States, travel only within the Western Hemisphere, and return to the same U.S. port on the same ship may present a government issued photo identification, along with proof of citizenship (an original or copy of his or her birth certificate, a Consular report of Birth Abroad, or a Certificate of Naturalization). Please be aware that you may still be required to present a passport to enter the foreign countries your cruise ship is visiting. Check with your cruise line to ensure you have the appropriate documents.
Children: Beginning June 1, 2009, U.S. and Canadian citizen children under age 16 arriving by land or sea from contiguous territory may also present an original or copy of his or her birth certificate, a Consular Report of Birth Abroad, a Naturalization Certificate, or a Canadian Citizenship Card.
