Employees may ask for age verification at any point, so please travel with a copy or original form of any government-issued ID, such as a birth certificate or passport for your child. A medical release for travel is required for any infant under 14 days old.

For the vast majority of adult travelers (ages 18 and older) flying domestically within the United States on Southwest Airlines, a birth certificate is not an acceptable form of identification at the TSA security checkpoint. Instead, adults must present a valid government-issued photo ID, such as a driver's license, passport, or military ID. However, a birth certificate becomes a critical document for Lap Children (infants under the age of two). Southwest is known for its "Lap Child" policy, which allows children under two to fly for free on a parent's lap, but the airline strictly requires proof of age to verify the child is actually under the age limit. In this specific case, a government-issued birth certificate (original or a copy) is the primary document used to validate the infant's age during check-in. Furthermore, if a minor is traveling alone as an Unaccompanied Minor, Southwest may request a birth certificate to verify their identity and age before they are allowed to board. For international flights to destinations like Mexico or the Caribbean, a birth certificate is never sufficient for any age group; a valid passport book is mandatory for all passengers.