I created two different letters, one for boys and one for girls, and each one comes with a proper envelope, already addressed to Santa!
You just need to choose which one you want:
Click here for the boys version.
Click here for the girls version.
Each file has two pages (one for the letter and one for the envelope). Print them on a color printer. Once the letter is filled in, cut around the envelope edges (the outer gray border), fold over the other horizontal gray line (below Santa's address) and glue the sides.
Fold the letter. place in inside the envelope, and then close the flap.
Mail the letters to Santa and check below your Christmas tree in a couple of weeks!
Have a wonderful weekend!