If he’s smart, in the fourth grade, and a good reader—I’d bet that he already knows about Santa Claus. Now, it’s always possible that he’s trying to shelter you from that truth....
If he knows, I suspect that it has less to do with “protecting” me and more to do with the fact that he gets the same kick out of putting on the show for his little sister that I do.
I also expect that we will have a talk on the subject after this Christmas.