In lord of the flies how did the boys come to be on the island?

In chapter three: Huts on the beach the lure of hunting, play and bathing have distracted most of the boys away from the necessary task of building shelters. The failure on the part of Jack to comprehend the annoyance and unfairness that his excessive preoccupation with hunting is causing to Ralph, who has gamely stuck to the task of building shelters, begins to drive a wedge between the two boys as their differing priorities become increasingly apparent.