I have journals that I share with each of my daughters. We call it a Journal Share and we take turns writing to each other. After we write, we leave the journal somewhere (usually under the bed pillow) that only the other person will find. The key to these journals being successful (for my family) is that each daughter knows that the journal is only for her eyes and my eyes. No one else can read what we wrote.
There are no rules (beyond not reading other people's journals). The girls are free to write whatever they want. We ask questions and answer questions. We share dreams... and fears. We talk about goals. And we talk about all the reasons we love each other! It is so fun! Sometimes we get on a good roll and write regularly... other times we may go several days, a week even, between writing. It is a flexible, no pressure tradition!
And I love it.
The above journals are from Whimsy Press.