Five Children and It : Psammead #1

Like Nesbit's The Railway Children, the story begins when a group of children move from London to the countryside of Kent. The five children – Cyril, Anthea, Robert, Jane, and their baby brother, known as the Lamb – are playing in a gravel pit when they uncover a rather grumpy, ugly, and occasionally malevolent Psammead or sand-fairy, who has the ability to grant wishes. He persuades the children to take one wish each day to be shared among them, with the caveat that the wishes will turn to stone at sunset.