If you are new to this series, especially if you are going to read it to a child, DO NOT READ THEM IN CHRONOLOGICAL ORDER! A child will lose interest after a few chapters. Few great stories are told strictly in chronological order and the hook for Narnia is "The Lion, The Witch, and The Wardrobe".
Many of these other reviews done by people saying that they like reading these books in chronological order are adults who fell in love with the series years ago, and now see this new order as making better grown-up sense. Reading it this way for the first time will leave you with many details that shouldn't be discovered until after reading the first few books in the original order, and won't keep a child interested the way I and so many others were as kids.
So please, if you are an adult familiar and returning to this series, feel free to read it in any order you choose, (I certainly do) but if this is your first time, read it in the order below...cheers
1) The Lion, The Witch, and The Wardrobe, 2) Prince Caspian, 3)The Voyage of the Dawn Treader, 4) The Silver Chair, 5) The Horse and His Boy, 6) The Magician's Nephew, and 7) The Last Battle