What is the importance of the "little people" in the novel, The Wonder?

In the novel, the "little people" symbolize much of what cannot be known. Many of the rituals that the O'Donnells--particularly Kitty--follow are intended to pacify them. Each evening Kitty leaves a saucer of milk in the living room so that they will not be offended, and Kitty tells Lib that she should put salt on her porridge so that the little people will stay away from it.