Or, though I'm not sure this would actually turn out like that, you could give them a massive sense of superiority of Not Believing In All That.

I knew somebody who was brought up by very Strict and Particular Atheist Humanists (I also knew her mother but this never arose in the course of our interactions) and they did Not Do Christmas, treated it like an ordinary day. For some reason this actually got reported in the local paper, but as this was Hampstead or Hampstead-adjacent I don't know why it was even news.