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 flights within the United States, children under the age of 18 typically do not need a birth certificate or any form of government-issued photo ID to pass through TSA security. The TSA accepts the identification of the accompanying adult on behalf of the minor. However, there are two important exceptions to this rule. First, if a child is flying as a "Lap Infant" (under age 2), many airlines—including Southwest and American—require a birth certificate as proof of age to ensure the child is eligible to fly for free or at a reduced infant rate. Second, if a child is traveling as an Unaccompanied Minor, some airlines may require a form of identification, such as a birth certificate or passport, during the check-in process to verify the child's identity and age. For international travel, the rules are much stricter: every traveler, regardless of age, must have a valid passport or, in some specific cases for travel to Canada or Mexico by land/sea for those under 16, an original birth certificate. To avoid any potential delays at the gate, it is always a "best practice" to carry a digital or physical copy of the child's birth certificate when traveling, just in case of unexpected airline-specific documentation requests.