One dealer worked out a deal with a local mall that provides a place for children to stay while parents are shopping. The mall bought 200 Santa Letters to give to the children. On the "Letter from" line, she typed in "Your friends at Gotham City Mall..." This would work for your day care centers as well.
A dealer's local town has a revitalization project involving the downtown area. The Revitalization Association provided "mail" boxes for the dealer to collect orders for Christmas letters from Santa for $2.25. The dealer printed the letters and started mailing them December 15.
If you would like to send Santa letters postmarked "The North Pole", check with your local postal service. They usually have a mail receptacle for this purpose.
The personalized letters can also be used as a marketing tool to promote higher average order sizes. "Buy 3 or more books and we'll include one of our personalized letters from Santa for FREE"