I have no idea where you have even come across the notion that he's not real, certainly not at home. Perhaps at kindy from children with other siblings.
You are really excited for Christmas though, but it's a long month of waiting and I think perhaps you are even beginning to doubt it will happen at all. For the first few days of December you asked me "is today Christmas?" But after several no's you've stopped asking. I just hope you'll be pleasantly surprised come Christmas morning and that will wash away your inner sceptic.