In the aviation industry, a child’s age on the date of travel determines their ticketing category. If your child is an "infant" (under 2) on the outbound journey but turns 2 before the return leg, most airlines require you to purchase a full child’s fare seat for that return flight. FAA and international safety regulations mandate that any child who has reached their second birthday must occupy their own seat with a certified safety belt during takeoff, landing, and turbulence. While some airlines may allow you to book the outbound as a "lap child" and the return as a seated passenger on a single ticket, others may require a seat for the entire journey to maintain consistency. It is critical to notify the airline during the booking process to avoid being denied boarding at the gate on your way home. In 2026, many digital booking systems now automatically flag these age transitions based on the birthdate entered, ensuring you are charged the correct prorated fare and that a seat is properly allocated for the second half of your trip.