Pillywiggins and the tree witch - Julia Jarman

When Natasha moves to a new house, she discovers a statue of a fairy in her garden beneath a huge menacing fir tree, which Natasha is sure is a witch. Gradually, with the help of a local boy, she unravels an ancient story that fairies stole the witch's baby and as revenge she turned a fairy to stone. Natasha realises that the only way to free the stone fairy, Pillywiggins, is to go into Fairy Land herself and rescue the witch's baby. But legend says that any human who enters Fairy Land may age decades or never come out at all.