Santa doesn’t exist any more than do Hobbits or pixies but they’re fun exercising our imaginations. What’s wrong with that and a temporary suspension of rationality? Killjoy.
When my son, who turned 30 two weeks ago, was 3, he asked me if there really was a Santa Claus. I quietly and matter-of-factly told him no, Santa was a person we made up to help us celebrate Christmas. He said "OK," and left the room. Ten minutes later he came back into the room, and proceeded to tell me everything Santa was going to bring him for Christmas, and I didn't try to dissuade him; he never understood what "Santa doesn't exist" meant for another four years.
The biggest mistake my parents made--and I know it was their biggest mistake, because they told me so--was that they taught my sister and me that Santa not only brought the presents, but he brought the decorated tree as well. This led to about ten years where my parents had to set up, decorate, and place the gifts under the tree after their two children had gone to bed on Christmas Eve.