How can the Elves start making toys, before children have sent their letters to Father Christmas?
That's a great question!
When Small Folk make a wish, it rises like hot air to the top of the world, where they collect and form the Northern Wishing Lights. A very special elf called Wish has the magical power to see individual wishes in the sky, and she can then inform the Lapland Toy Factory of all the Small Folk wishes she has collected - This way they never fall behind in their toymaking.
When Father Christmas (or The Toy Maker as he still calls himself) then receives a letter from a child, he can select the correct toys from the many that the Elves have already made. It's really rather clever!