Tasha Tudor's Letters and Valentines for dolls arriving via the Sparrow Post.
From what I can understand, Ms. Tudor had the
letters going back and forth between her own dolls using this imaginary post office.
What a fun idea! It would be easy enough to make tiny, tiny letters or cards, and 'post' them
near the bird feeder for kindly birds to deliver.
Finding the letters gone, the children would certainly believe them to be on the way to
whomever they had been addressed.
But who could be posting back???
A storybook character?
A far-away grandparent?
The birds themselves?
I can imagine their excitement when they find an answering eensy letter waiting for them
by the bird feeder!
(Tolkien's Letters From Father Christmas - Tolkien writing letters from Santa to his children.)