It just wouldn't work. I think the key thing is a book has to work even if it's not funny. It should be possible to write it so that it would work even if it had no jokes in it. If it's simply relying on the jokes all the way through, its sole reason for existing, then it's not likely to achieve very much. And the interesting thing about the magic of childhood, it's a phrase that only adults would ever dream of using.
Children know the world is a far more dangerous place than adults can possibly believe.
It's also a book about winter, and the mythology of winter. As I'm sure you know, a lot of the things that we celebrate around the dark of the year, and a lot of the decorations, and even some of the songs, had their roots in a tradition that goes all the way back beyond Jesus Christ and possibly even back beyond the building of Stonehenge. We are meddling with dark magic at the dark time of the year. I also noticed a subtext about belief. That's one that's been woven through quite a few of the Discworld novels.