A Wrinkle in Time by Madeleine L'Engle is one of my favorite books from childhood. In this story two children, Meg and Charles Wallace, along with their friend Calvin, meet three extraordinary extra-terrestrials who take them on a journey to save their father who is being held prisoner on another planet. The children must learn to use both their strengths and their faults and think outside the box in order to succeed in their mission.
I would consider this story to be a combination of science fiction and fantasy. Although the methods of space travel are based in scientific theory, there really isn't any explanation for how it is supposed to work or any technological devices used, so the effect is pretty much the equivalent of magical teleportation. I enjoyed reading this book nearly as much as an adult as I did when I was a child. In some ways I got even more out of it as an adult since I understand many of the scientific concepts talked about in the book much better now.
The only thing that bugs me about this book at this point in my life is the overt Judeo-Christian themes present in some places in the story. It would have been nice if the author could have stuck with the basic good vs. evil theme without bringing religion into it. I don't necessarily mind spiritual themes in the books I read, but it just felt like a bit much when it was implied that the characters were chosen for a mission by God, especially in what is supposed to be a science fiction story. Though if I recall correctly, the author also uses religious themes in other books in the series as well. In any case I felt that as much as it bugged me, that I could overlook these details in a book that is a childhood favorite, and it didn't spoil my enjoyment of the book too much. I would strongly recommend this book to both children and adults as it contains some very powerful messages in addition to being a great science fiction adventure story.