When I was working for a summer camp for 8th and 9th graders, I was sent to the airport to make sure that all the kids got on their planes. About half of them were traveling as unaccompanied minors. When I got to the airport, the person for the camp coordinating our airport operations (trust me, when you're trying to get 150 kids on flights all in an 8 hour span, you need someone to do that) told me to pick a name from this list, go up to the ticket counter, and tell them that I was escorting that child to the gate. They printed a security pass, which the TSA took at the checkpoint and I went through security just like any other passenger.
My point is that it's particularly easy if you pretend to be escorting a child.