What is the importance of the "Giganticus Plan" in the novel, The Witches?

The Giganticus Plan is the Grand High Witch’s plan to eliminate all children in the world, beginning with a trial in England. The Giganticus Plan involves the witches quitting their day jobs, purchasing sweet shops, and having a day of grand openings where free candy will be given to children. The candy will be laced with Formula 86, which will turn the children into mice after which time the adults of the world will kill the children. The Giganticus Plan is to be enacted upon the conclusion of the annual English witches’ retreat.