Trivia: Before filming the Narnia scenes, Georgie Henley was never shown the set. To get a genuine reaction of surprise, director Andrew Adamson had Henley brought onto the Narnia set blindfolded. Her reactions to Mr. Tumnus are real, too. Before filming their scenes together, she had never seen James McAvoy in costume.
Trivia: After the initial credits begin (since many people leave the theatre as soon as the credits appear, they miss this), there is an additional short scene between Professor Kirke and Lucy, that takes place near the wardrobe. (02:12:25)
Trivia: Georgie Henley (Lucy) created a bucket on set called "The Potty Mouth Bucket," and anyone who swore would have to pay a certain amount to the bucket. James McAvoy and Skander Keyes were reportedly the biggest offenders.
Trivia: When the children listen to a news report on the radio, in Professor Kirke's house, the voice belongs to Douglas Gresham, who is C.S. Lewis's stepson, and co-producer of the film. C.S. Lewis, author of the original novel, delivered radio addresses over the BBC during World War II.
Trivia: In the scene where Edmund and Lucy go through the wardrobe, they needed a shot of Edmund's feet walking through the wardrobe. Since Skandar Keynes (Edmund) was gone for the day, Anna Popplewell (Susan) put on Edmund's clothes from the waist down and portrayed his feet for this one shot.
Trivia: The famous lamppost has roots on the bottom. They did this because in the first book (The Magician's Nephew) it is explained that the lamppost grew out of the ground.
Trivia: At the train station, Peter glances at a certain soldier. The person portraying the soldier is Jaxin Hall, the actor who lost the role of Peter when they cast William Mosley as the eldest.
Trivia: In the scene where Susan runs in with Aslan and the rest of the army she pulls her bow back and the shot ends. When they were filming she was so "in the moment" that she let the arrow fly. By the end of production the crew still hadn't found it. Apparently it is still there waiting for some very adventurous fan to climb up and find it.
Trivia: Georgie Henley's older sister, Rachael, plays Lucy as a young woman. (02:10:00)
Trivia: The magical wardrobe has carvings that tell the story of "The Magician's Nephew" (Chronologically, the first book in the series).
Trivia: The wardrobe that C.S. Lewis based the story on can be seen at Wheaton College in Wheaton, Illinois.
Trivia: When the Pevensies are telling the Professor of their doubts about Lucy and her tales of Narnia, he proposes three possible conclusions: that Lucy is either crazy, lying, or telling the truth. C. S. Lewis famously proposed these very same options as what he dubbed "The Trilemma of Jesus", focusing on whether He was lunatic, liar or Lord.
Trivia: Some of the Pevensies' family history is based upon the four actors. Their mother, Helen, is named after Georgie Henley's mother, and Susan comments that they're from Finchley, where Anna Popplewell is from.
Trivia: In the final battle, the White Witch's fur collar is made from Aslan's mane, shaven off the night before.
Trivia: The photo of Mr. Pevensie which Edmund tries to retrieve during the air-raid sequence is a real-life picture of editor Sim-Evan Jones' father.
Trivia: The two children who share a car during the train sequence are Cassie Cook and Brandon Cook. They are the children of actress Sophie Cook, who had portrayed Susan Pevensie in the TV mini-series, The Lion, the Witch and the Wardrobe.
Answer: Spoiler alert: this gives some important plot twists away. Sometimes a bit of unresolved mystery improves a story, and I think this is the case here. But the book partly answers your questions. At the end of the last chapter it is shown that Mrs MacReady thinks the wardrobe is just a piece of furniture. She knows nothing about Narnia. But Professor Kirke amazes Peter, Edmund, Susan and Lucy by expressing familiarity with Narnia and explaining that a wardrobe might well be a portal into Narnia. If C S Lewis had not written any more books after completing "The Lion The Witch And The Wardrobe" Professor Kirke's knowledge of Narnia would probably have been an unresolved mystery. But C S Lewis later wrote "The Magician's Nephew" which tells how Professor Kirke visited Narnia as a boy. The final chapter of this book says he took an apple back with him, which he planted in his garden. It grew into a tree, was cut down and made into the wardrobe. So Professor Kirke was not consciously aware of what the wardrobe could do, but with hindsight, he realised that he had set up a chain of events that caused the children to discover Narnia.