What do you mean Father Christmas isn't real? The nonsense people swallow these days...
Every Christmas time normally rational and dull people start behaving in a weird way, smiling at total strangers, giving presents to each other, spending time with people they want tospend time with, and giving time to people they normally avoid. And so forth.
The idea that we all get taken over by a benevolent Christmas Spirit with an objective existence seems quite a reasonable one.
If you want to draw a picture of it, an elderly gentleman with a white beard seems quite a reasonable one to me. Maybe I'm prejudiced because I am myself an elderly gentleman with a white beard, and I get some very thoughtful glances from passing children round this time of year.
I believe in Father Christmas in the same way that I believe in Christmas. Which is the same way that Americans, I understand, believe in Thanksgiving - and a Happy Thanksgiving to all of you over there.