The setting itself, is of course, constructed by Golding. The middle of a nuclear exchange, that is likely destroying much of the known world, has led the parents of the children on the plane to send them off somewhere presumably safer.
This is, of course, a fictional parallel to the real story of "Operation Pied Piper," in which millions of people, many of them children, were evacuated from the heavily populated areas of England, in order to prevent them from becoming casualties in the expected bombings. Children were evacuated to rural areas and also to New Zealand, Australia and other places in the British Commonwealth that were thought to be safer.
Though sometimes the results were traumatic, generally the program was seen favorably. Of course the results that awaited the boys on the island were less than ideal!