All these Christian groups out to exploit the Christian message of the Narnia stories have completely missed the point, actually undermining the power of the stories as propaganda for them.
The point was that one should read the stories as a child, and love them, possibly rereading repeatedly into young 'adulthood', without being aware of the Christian message. Their power as tools of moral formation is most effective in this way. The later discovery of the the clear Christian allegory becomes a powerful moment in an individual's moral, religious or philosophical development.
I should add, this is a double-edged sword. I've seeen committed, active Christians, deep lovers of the Narnia stories since childhood, who had never been aware of its religious payload, and felt the underpinnings of their religious certainty shake just a little when they were informed of it.
Shepherding in the kids into the movie, explicitly informing them of the Christian message they are about to imbibe, completely undermines the power of this wonderful piece of allegorical literature. After all, if it was that easy, there was no need for him to write the books in the first place.
Thankfully, it isn't that easy. Although in his time, Lewis was surprised by how few recognised the stories for what they were, and at how easy it had been to "smuggle" Christian propaganda in the guise of fiction.
Still, accident has a role in all good art.