In the movie narnia: Prince Caspian why do lucy and edmound stay in narnia but not peter and susan?

As stated above, Peter and Susan have learned all they can from Narnia. CS Lewis wrote these books as explanations of the Bible for children. At the end of the book, Aslan tells Susan and Peter that they must get to know him in their own world. Aslan, the God-figure, is telling them that they must find a relationship with God in the real world now that they have a tangible understanding of him as Aslan. Edmund and Lucy, being younger, still need this tangible God-figure in their lives.