What happens when you tell a child that Santa Clause isn't real? They freak out. Why? Because they believe that Santa will give them toys if they are good. No Santa means no toys. A child will just kick and cry over the loss of their Santa, while an adult will terrorize and force people to believe, rape women, and blow up buildings.
If you allow the child to come the realization independently and answer their question about the existence of Santa with the question "What do you think?" a dialogue can develope where the idea of Santa isn't destroyed but morphed into a philosophy of giving. Children being the instinctively clever little beings they are come to the conclusion that parents are Santa.
I was taught a concept of Santa being a feeling that I can hold onto that lets me see need and try to fulfill it. I still like to imagine the North Pole and elves but I relish the ability and opportunities to be the Santa for someone when I can. The myth can become the religion that way.