You and your partner must make a pact. A pinky swear to keep a secret to the depths of your graves. Tell no one the deeds you are about to embark upon. You have the note card and pen, right? You need only one card to begin this writing voyage together. However, in the days to come, you'll want to have a surplus on hand to keep this quirky correspondence with one another going.
First you two must decide upon a place for notecard exchange, a sort of 'X marks the spot', if you will. Under a rug? Behind a chair? Near the dog bowl? Hmmmm, probably not. On the bookshelf? Yeah...that's a good idea. Decide on a place where notes can be occasionally hidden. Not every single day, mind you. Our game would get old then. One person writes a note and hides it. The private pen pal sneaks about, snags it from the designated spot, then finds a quiet place to read it. Now it is their turn to correspond!
Write silly jokes, light-hearted comments about work or school, find some specific wonderful attribute to praise, or express your affection for one another. Slip a little flower bud between the folds of the card. Maybe a handmade book mark or a nice piece of stiff, pink, cardboard-like bubble-gum. Simple treasures to be shared. Precious memories to cherish forever.
I have found that this game is particularily helpful when a parent has to travel frequently or shares custody of a child. Playing Private Pen Pals helps to ease the burning ache of absence from one another in a fun, simply silly way.
Warning, parent! This is not a time to lament over invented spellings. For now, enjoy your child's message. We'll work on that spelling later.