In many holiday movies where Santa does exist, how do the parents not know?

I’m talking about movies where there is a real Santa that brings presents to all the kids in the world. The kids believe in him, but obviously the parents have “known” for a while that he isn’t real. Yet, every Christmas children receive presents from Santa. How come the parents don’t notice presents from this “real” Santa, shouldn’t they actually know he is a real person? This is a major plot hole!