In Chapter 5 of "Lord of the Flies," why shouldn't the littluns go near the fruit?

It's not that the littluns shouldn't go near the fruit at all, but that they need to stay away from it when they go to the bathroom. Ralph reminds them that they need to use the rocks that get washed by the tide when they are "taken short." The littuns are being lazy and going wherever they want, another sign that the boys' civilization is deteriorating.