Five Children and It by Edith Nesbit

To Cyril, Anthea, Robert, Jane, and their baby brother, the house in the country promises a summer of freedom and play. But when they accidently uncover an accident Psammead--or Sand-fairy--who has the power to make wishes come true, they find themselves having the holiday of a lifetime, sharing one thrilling adventure after another.

Asleep since dinosaurs roamed the earth, the ill-tempered, odd--looking Psammead --with his spider-shaped body, bat's ears, and snail's eyes --grudgingly agrees to grant the children one wish per day. Soon, though the children discover that their wishes have a tendancy to turn out quite differnetly than expected. Whatever they wish whether it's to fly like a bird, live in a mighty castle, or have an immense fortune --something goes terribly wrong, hilariously wrong.

Then an accidental wish has horrible consequences, and the children are faced with a difficult choice: to let an innoncent manbe charged with a crime or to lose for all time their gift of magical wishes. Five Children and It is one of E. Nesbit's most beloved tales of enchantment.