Father Christmas believes in the old fashioned magic of Christmas, writing to your children with his best quill pen to involve them with his adventures in the North Pole. He gets a bit carried away, and puts little drawings in too. 
After he's carefully written your child's name (and put in a wee well done for their special achievement), he folds it up, like a proper old fashioned letter, writes the address of where they'll be when they find it (e.g. 'Oliver, in mummy and daddy's bed, at the house with the trampoline", and seals it with a drop of sealing wax.
It's a lovely way to bring a touch of old fashioned magic to Christmas.
He can also write your words out in his own beautiful style - ideal if you are spending Christmas away, or have a special message for your children.