In a summary of his novel, William Golding stated that the characters of "Lord of the Flies" are symbolic. Piggy, for example, represents the rational side of man while Roger is the malevolent side that can only be controlled by the conditioning of society.
The littl'uns--often grouped as one--represent various stages of innocence and unbridled fear. Little Henry, for instance, represents the trusting stage of innocence as he sits alone on the beach, transfixed by the tiny creatures who venture onto the shore. When stones land near him, he does not cry or run, for he has no knowledge of the evil in man's heart as represented by Roger, who hurls the stones to terrorize him. In contrast to Henry, Percival Wemys Madison represents the terror of innocence when faced with strange unknowns. When he believes that he sees the beast in the ocean, he breaks down and cries. As his fright of the unknown overpowers him, he cries all the time, until he is so shaken that he cannot even recall his own name.
Another character, Johnny, represents the belligerent child, sturdy and argumentative. Robert, who is not quite a "big'un," represents the younger boy wants to be accepted by the older ones, the hunters; however, when he pretends to be a boar so they can practice the hunt, he is hurt as the dance excites the others to wildness and ferocity. Finally, the boy with the mulberry birthmark, who disappears one night may represent the loss of innocence on the island.
To me, the main purpose of the littleuns is to provide situations and characters for the bigger kids to interact with.
Perhaps one of the most obvious ways in which this happens is when the littleun with the mulberry marking on his face tells them about the beast. It is the littleuns in general who give the beast its initial life.
The littleuns also help show what the big kids are really like. A good example of this is when Roger throws the rocks at Henry but purposely misses. This gives us a good look at Roger's state of mind at that time.
So overall, I think the littleuns are mostly there to help us understand what the big kids are really like.
One of the major themes that Golding tackles in Lord of the Flies is the loss of innocence. I believe he uses the littluns to bring this theme to light for his reader. Even though we do not know how many littluns are actually on the island, our narrator does tell us that all of the children range in age from 6-12. That being said, can you really imagine a little six-year-old boy running around with a bunch of older boys who have war paint on their faces and a spear in their hands? That's not how I usually picture a little boy, but after Jack and the other hunters take control of the island, the littleuns are no longer the civilized, innocent little boys they were before crashing on the island. They are now part of a savage, uncivilized group of boys who not only go around spearing pigs, but who also do physical harm to one another.
When someone (or a group of young kids) are referred to as one thing (the littl-uns) doesn't that show and display their unimportance? ...