What is the true reading order of The Chronicles of Narnia?

Well, when you say "true reading order" it is uncertain what you mean. The way the books are published now, the books are presented chronologically, so the first part of the story, historically, happens first, and so on. The only other order you could go with as "true" (at least in my mind) is the order that C.S. Lewis actually wrote the books.

In the first scenario, you would read "The Magician's Nephew" first, and in the second, you would read "The Lion, the Witch, and the Wardrobe" first.

C.S. Lewis himself said that it probably didn't matter in which order they were read... however, as a personal observation, I think reading them in the order in which they were written works better. I think you fail to notice story discontinuity that way, because you are going along as the author did. When you read them in the other order, it is easier to find things that don't quite match up... so, if your mind works that way, you might want to read them in the order they were written.

The actual order in which the Chronicles of Narnia were written, and originally published by MacMillan is:

• 1950: The Lion, the Witch and the Wardrobe
• 1951: Prince Caspian
• 1952: The Voyage of the Dawn Treader
• 1953: The Silver Chair
• 1954: The Horse and His Boy
• 1955: The Magician's Nephew
• 1956: The Last Battle

When Harper-Collins took over publication, Lewis's stepson Douglas Gresham recommended they be published according to Narnian chronology. Thus, the new order became:

1. The Magicians Nephew

2. The Lion the Witch and the Wardrobe

3. The Horse and His Boy

4. Prince Caspian

5. The Voyage of the Dawn Treader

6. The Silver Chair

7. The Last Battle
Four children, Peter, Susan, Edmund and Lucy are evacuated to the country in World War 2. They stay in a large house owned by an old Professor. First Lucy, then Edmund, then all four children find their way through an old wardrobe into Narnia, a magical land with talking animals and mythical creatures such as fauns and dwarves. But Narnia is held under a magical spell by the evil White Witch to ensure it's always winter but never Christmas. The children have to battle evil creatures and deal with betrayal and treachery but make many good friends as well. Finally, with the help of Aslan (The Lion) they defeat the evil witch and spring and freedom come back to Narnia.