Assuming the tween is flying alone, they will need to have all of the necessary documents in order to board the plane. This includes a passport or other government-issued ID, as well as a boarding pass. If they are traveling with someone else, they will also need that person's ID and boarding pass. In addition to these items, it is always a good idea to bring along any medication that might be needed during the flight, as well as snacks and drinks in case the airline does not provide them. A book or other form of entertainment can also be helpful for long flights.