Just incase you haven't come across them, it's These. You get a set of 24 letters with your kids names on and then you deliver one a day through advent. Last letter is on Christmas Eve. The envelopes have their names on too and an International Elf Service stamp.
They are absolutely gorgeous - the paper is quite thick, a bit creamy coloured and has various different 'bits' in and feels textured. The illustrations look like they've actually been painted on almost and it all feels really authentic. Really lovely packaging and they just look and feel special. A real keepsake.
I can't WAIT until the 1st December 
. My kids are going to explode, as am I.