An example of a properly addressed letter. Write Santa's mailing address on the envelope.Write a personalized response to the child's letter and sign it "From Santa. " Insert both letters into an envelope, and address it to the child. Simply fill out the "To:" section with your child's name and address. For the "From:", add Santa's name and North Pole. 1) Pick up your "Letters to Santa" form at any Little Free Library location in Fairfax. Mention the child's age in the letter as well. Mention their name in the body of the letter at least twice in addition to addressing it to the specific child. Get a personalized letter from Santa for your child!