What is the turning point of Narnia?

It is a about a family of children, who are sisters and brothers, who stumble upon a magical wardrobe that takes to a magical place called Narnia. There they met an evil ice queen who they must defeat in battle, a lion that helps them, and other magical creatures. After beating the witch and her army in battle, they return home to discover that the many years they were away in Narnia was only a day in the real world.