"We dare not harm this little girl," he said to them, "for she is protected by the Power of Good, and that is greater than the Power of Evil. All we can do is to carry her to the castle of the Wicked Witch and leave her there." (Baum Ch. 12)
I think this quote shows the established rule of thumb for most children's literature; "Good is stronger than evil." This notion is virtually omnipresent in all children's literature and caters to their innocence and naivete. As soon as I read this quote (cheesey as it may sound) I felt like I was reading it as a child. The Wizard of Oz caters to that innocent, hopeful part of us that we were so in touch with as children and seemed to have lost along the way.