Extremely Lengthy Creation: C. S. Lewis first pictured the faun from The Lion, the Witch, and the Wardrobe when he was sixteen. He did not begin to write the story until he was forty, and finally finished the book when he was fifty.
Keep Circulating the Tapes: For most their publishing history, the books were numbered in publishing order (LWW, PC, VDT, SC, HHB, MN, LB), with internal chronology bouncing around as the series is read. But since 1994, publishers (beginning with Harper Collins), began re-numbering the series to fit the story's internal chronology (MN, LWW, HHB, PC, VDT, SC, LB), which mixed up the publishing order. Because of this, older volumes of the series that maintain the classic numbering go for a lot more money today than they once did.
Torch the Franchise and Run: The final novel, The Last Battle, ends with all the main human characters (except Susan) dying in a train accident and being instantly transported away to the afterlife by Aslan, and Aslan subsequently obliterating Narnia from existence (similar to the end of Star Trek III: The Search for Spock). It was quite clear that C. S. Lewis wasn't planning to ever write another Narnia novel.
Channel Hop: The films jumped from Disney to 20th Century Fox to Sony and eOne.
The Danza: A minor one. Edmund's horse Phillip is voiced by Phillip Steuer.
Dyeing for Your Art: A minor case. Georgie Henley's hair was actually lightened for the film (as Lucy is a blonde in the book) but it's not that noticeable.
To create the right slightly creeped out vibe between the characters, Tilda Swinton (who played the White Witch) would spend time in between shots subtly hitting on Skandar Keynes. Who would have been around 14 at the time.
The four principals were not shown the snowy Narnia soundstage until they were filmed first entering it from the wardrobe, so that their awestruck expressions would be genuine. Georgie Henley was blindfolded before her own first entry into Narnia.
In a bit of a meta case, the film was shot in as close to chronological order as possible (as opposed to a normal filming regimen, which is scheduled based on when sets are available and so on), so that the childrens' emotional growth onscreen would be reflected by their physical growth throughout the shoot.
Follow the Leader: The Narnia books had been adapted into live-action before the film series, but the film series itself came in the wake of the movie versions of Harry Potter and particularly The Lord of the Rings (the original being written by Lewis's fellow InklingJ. R. R. Tolkien). Just like (and probably because of) the latter, the battle scenes are considerably beefed up compared to the books.
Quietly Cancelled: Initially beginning with a $700 million debut with The Lion, the Witch, and the Wardrobe, the sky was the limit for Disney and Walden Media's films, which seemed destined to compete with The Lord of the Rings and Harry Potter film series. However, after Prince Caspian didn't make quite as much as Disney liked (only $400 million), they quietly canceled The Voyage of the Dawn Treader until 20th Century Fox picked up the rights and made the film on a lower budget, with an equal return to Prince Caspian. After mutterings of The Silver Chair being a reboot, talk disappeared completely until Netflix announced they were making a new series of their own in 2018.
Kill Six Billion Demons. When heroine Allison returns to our world after an unwanted excursion to the parallel reality of Throne, one of her friends says "Because if you have been to Narnia, you better tell me."
In Lost Voices, Luce overhears the human Tessa telling her mother how she tricked Anais, who never reads anything, into thinking that Peter turns out to be a vampire who eats Lucy at the end of Prince Caspian.
So My Kids Can Watch: Makeup effects artist Howard Berger, whose prior credits include Hostel and Sin City, mentioned in an interview that this would be the first movie he worked on that his kids could watch. He later won an Oscar for his work.
