I'm self employed and work from home a lot. I have a small whiteboard stuck to the wall near my desk which my son Patrick enjoys writing on. So I bought another mini whiteboard for him. I hadn't planned it - but gradually the whole family has starting writing little messages on his whiteboard. As my children grow up (I also have two teenage daughters) they're leading increasingly independent lives and we seem to all be in the house at the same time less and less. The whiteboard provides a simple and direct way to chat asynchronously. And I think that helps them express themselves more freely.
I also bought a divers slate so I could jot ideas down as they come to me in the shower. They've adopted that too!