How can the littuns in Lord of the Flies be described?

The litluns are the younger boys on the island. There seems to be no specific age at which a boy is classed as either a littlun or a biggun. Simon, Robert and Maurice are apparently in the undefined area between both but are generally included in the ranks of the bigguns. The undisputed littluns are decribed physically as being "..very brown and filthily dirty." The live an almost completely separate life to the bigguns, filled with their own concerns and games. They attend the meetings because Ralph is old enough for some of them to identify him with adulthood and also because it provides entertainment. They spend most of the days eating fruit and suffering from chronic diarrhoea, as a consequence of eating unripe fruit. They play on the sand and sleep in the shelters, are homesick and their nights are tormented by nightmares and fears of the dark.