I have children, too, three of whom are about the age of King's daughter. After a lifetime of flying with me, they KNOW that we are to be AT THE GATE when boarding begins, let alone at the 15-minute mark. If one of my children had insisted on leaving the gate for any reason so close to boarding, I would have given him or her the appropriate boarding pass, and the rest of us would have gotten on board!
Having said that, and with the additional assumption that King is describing the agents' behavior reasonably accurately, I would fire both of them immediately. I don't care how much King might have annoyed them; their behavior cannot be tolerated. I wonder if anyone in South Bend can let us know what happens as a result of this incident.
Bruce