At check-in, the airline will require the adult who brings the child to the airport to fill out a form that will have that adult's name, address and phone numbers on it, should the airline need to make contact after the child's flight leaves. Even more important, though, is that the form must show the exact name, address and phone number of the person who will be picking up the child at the destination airport. The airlines will not release the child into anyone else's custody. And, the person who picks up the child must be able to prove that he or she is the designated person. As long as we're talking about proof, you should be prepared to show proof of the child's age, should the airline require it.
Airlines usually give unaccompanied minors something to wear, such as a button or a badge.
When it is time to board the plane, airline employees help unaccompanied minors board first. That way, if the flight is delayed or canceled, the child won't be stranded at the airport. Bottled water, juice or snacks may be a good idea, too, just in case there is a long wait for those things on the plane.