Every US citizen, regardless of age, must have a passport to travel abroad. Newborn babies, infants, and toddlers all need a passport to leave and enter another country. Just as if an adult was applying for a passport, babies must have Form DS-11 filled out and submitted.

A 3-month-old infant can fly domestically within the same country (such as within the U.S., UK, or Australia) without a passport in 2026. For domestic flights, most airlines only require a birth certificate to verify that the child is under two years old (if traveling as a "lap infant"). However, for any international flight, a 3-month-old is legally required to have their own valid passport, regardless of the destination. There are no exceptions for age in international travel; even a newborn must have a passport and any required visas. In the U.S., parents should bring the infant's birth certificate for domestic travel just in case the airline gate agent requests proof of age to confirm the child qualifies for a free or discounted lap seat.