U.S. and Canadian citizen infants are not required to have a passport for travel by land or sea - although they are required to present a copy of a birth certificate and, if not traveling with both parents, the Department of State suggest a consent letter accompany the other parent(s) due to the rise in instances of ...
Consent to travel A child travel consent form has to be signed by both parents or legal guardians and has to contain: The child's basic information (name, gender, birthday, and place of birth) Both parents' or legal guardians' contact information. The traveling arrangements.
Children under 18 don't need an ID to fly domestically but do need a passport for international flights.