Hi, i'm not very good at this so wasn't sure whether to post it as a tip or product, sorry if i have done it wrong.
If your child writes a letter to santa address it to
Santa/Father Christmas, Santas Grotto, Reindeerland, SAN TA1.
Affix a first or second class stamp and post before the 11th December and Santa will send a free reply.
Royal mail try to respond to all the letters but cannot gurantee a reply so the earlier you can post the better.
Hope this helps someone.
Perhaps you should have a stand by ready as this isn't guaranteed, you can print drafts out from http://www.christmaslettertips.com/free_printable_santa_letters.htm