Typically, minors under the age of 18 do not have to present identification for domestic U.S. travel. Airlines will accept identification from the responsible adult on behalf of the minor(s). For international travel, minors under the age of 18 must present the same travel documents as the adult.

For domestic travel within the United States, United Airlines generally does not require identification for children under the age of 18. TSA and airline policies allow minors to fly without a photo ID when accompanied by an adult, though the adult must have their own valid identification. However, for international travel, children of all ages, including infants, must have a valid passport and any necessary visas for their destination. If you are flying with an "infant on lap" (under age 2), United may request a birth certificate at check-in to verify the child's age for fare eligibility. In cases where a child is traveling as an Unaccompanied Minor, specific paperwork and the identification of the adult dropping off and picking up the child are strictly required. It is always wise to carry a copy of the birth certificate even for domestic flights to avoid any boarding delays or disputes regarding age-related baggage or seating perks.