What happened to the six year old boy in the story Lord of the Flies?

There are an unspecified number of littluns who are aged around six but I am guessing that you are referring to the littlun with the mulberry coloured birthmark on his face. He was the boy who first mentioned the snake-thing or beastie, which he said he had seen during the night and which had tried to eat him. It is assumed that like all of the other boys he went to the top of the mountain to help to build the first fire. Many littluns got bored or tired of collecting wood and wandered off to pick fruit. After the fire was lit a cascade of sparks set fire to the same pocket of jungle from which the boys had gathered wood. This was the same area in which some of the littluns had looked for fruit. As the littlun with the birthmark on his face was never seen again it is probably safe to assume that he died, somewhere in the pocket of jungle, killed either by fire or by smoke.