You can tell by reading the first page of The Magician's Nephew "This is something that happened long ago when your grandfather was a child [...] I won't tell you..." that the story is actually written in the present tense. It is written like the narrator is sitting in front of you telling you this story. The narrator refers to himself in the first person as I. As he tells the story he mentions all the characters in the story and what they did. This part is in third-person because these events happened long ago. However, passed on the first page the narrator is telling the story from a first-person point of view.