Children 5 to 14 can travel alone, but you have to pay an un-accompanied child fee, to cover the cost of an airline employee escorting your child on and off the plane, and between gates if it's a connecting flight. Fees vary by airline but can really start to add up, especially on connecting flights. Due to all the extra stuff the airline needs, you must contact the airline to book, you can't (I don't think) do it on a web site. You can research and find the lowest fares and schedule info on the web, then call the airline to get their child policies, fees, and to book the tickets.