We saw Arthur Christmas last week too and I enjoyed it much more than I expected. The part I really liked regarding the Santa issue though, was Arthur's determination to get the little girl her gift and says several times, it doesn't matter who brings it, it just matters that every child gets a present from Santa. I thought that was a very clever way of putting it.
DS8 is still dedicated to the idea of Santa, although I fear the days are numbered. He said to me the other day, "You know how I know that Santa is real? Because we can see him from the satellites." NORAD has a website that "tracks" Santa that I showed him when he was little. The fact that he was searching for evidence suggests to me that perhaps is on to it but doesn't want to admit it. But now I have two myths to deal with: Santa and the idea that one can trust information that comes from the government.
When I was a child I found my Santa letters packed in a box in the garage. I was probably 7ish. But I never told my parents I found them and continued to pretend for several years after that. I just loved the Christmas magic and still do!