what is the purpose of the vignette about the three uns

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.