The Psammead Trilogy by Edith Nesbit
A great collection to include Five Children and It, The Phoenix and the Carpet and The Story of the Amulet. When Cyril, Anthea, Robert, Jane and their baby brother start exploring a gravel pit not far from their new countryside home, they make an unexpected and very curious discovery. The gravel pit is home to a Psammead, a sand fairy. This ugly creature has eyes like a snail, ears like a bat and the body of a spider, and is very grumpy indeed. He grants the children one wish every day, and though they are excited to have all their desires fulfilled, they soon realize that having one's wishes come true can have unexpected consequences... More adventures will follow in the other two books in the series