Whether a 2-year-old needs a passport for a cruise depends on the cruise's "loop" and the destination countries. For Closed-Loop Cruises (voyages that begin and end at the same U.S. port and travel only within the Western Hemisphere), a U.S. citizen child under age 16 typically only needs an original government-issued birth certificate. However, this is often a "minimum requirement" rather than a recommended practice. If the ship has an emergency and you need to fly home from a foreign port (like Cozumel or Nassau), you will be unable to board a plane without a valid passport for the child. Furthermore, some specific destinations like Martinique or certain South American ports may require a passport regardless of the cruise type. For any cruise departing from a foreign port (such as Barcelona or Vancouver), or a "One-Way" cruise (e.g., San Juan to Miami), a valid passport is mandatory for all passengers, including infants and 2-year-olds. It is generally advised to get the passport anyway to avoid potential boarding denials or travel complications in the event of an unexpected change in your itinerary or a personal emergency.