I have been sending my granddaughters, now age 5, fabric postcards each month for over a year now. I have always signed them as "Secret Admirer" so they call them their "Secret Admirer Cards". One puts them in a box and the other puts them between pages of a scrapbook. They look forward to them each month. Yesterday I mailed January's card.
On the back - "To enjoy the beauty of a snowflake one must stand outin the cold. Love, from a secret admirer."
And in December I embroidered angels. I don't remember now exactly what I wrote on the back.