Ahlberg, Janet & Allan "The Jolly Postman or Other People's Letters" - 1986
One of the favourite activity books my boys ever had. "The Jolly Postman" is full of letters and cards, letters from fairy ale and nursery rhyme characters. You can take the letters out of the envelopes and read them, they are all pretty funny and all of them nicely illustrated, as anything written by the couple. This book means hours and hours of fun with your children. When my boys sorted their books a couple of years ago between those to keep and those to give away, this was definitely a keeper.
The book is also a great way of introducing real letters to children, show them how you can write to a friend or relative far away and how happy they will be to receive your post.
From the back cover: "The Jolly Postman delivers cards and letters to various fairy-tale characters. He has a letter of apology for the three bears from Goldilocks, a postcard from Jack for the giant, a solicitor's letter on behalf of Little Red Riding-Hood for the wolf who ate grandma, and so on. There are six envelopes in the book, each containing letters, cards, etc."