Father Christmas (and he likes to write as Santa too) is very careful to write a letter to every child with his best quill pen, and he likes to put little pictures in the margin, like very old fashioned letters that your great grandparents might write - when a camera was a rare thing to have.
In your letter, your child’s name is handwritten with pen and ink as part of Santa’s uniquely illustrated Christmas letter. 
It’s printed on high quality parchment paper, folded the old fashioned way (just like Jane Austen would fold a letter), wax-sealed with Santa's jolly red ‘S’, and your child's name and magical Christmas address are handwritten with his big quill pen on the front.
Santa is happy to be 'Father Christmas' too.
It's a little special piece of magic to add to the wonder of Christmas, and a little keepsake to look over at future Christmasses.
Maybe your child finds it on the plate where the biscuits and carrot were, or under the tree, or maybe it falls out of the story book granny is about to read.
And of course we'll post them to wherever you are (The elves will help!).