I honestly don't think the vast majority of 4 year olds aren't going to have their belief destroyed by one kid telling them Santa isn't real. If they want to believe at that age, they will in the face of any opposition. And the ones prone to skepticism, like Ellie (and Casper) won't be wounded either. Let her say what she wants to say. I do like the "spirit of Christmas" workaround, though.