Talk to them openly about the parent, include both the parent and the child as much as you can in the lives of one another. There are so many programs out there now, for example the USO has United Through Reading where they record a parent who is deployed reading, and the book gets sent to the child so that they can read together. I am also a huge advocate for pictures, tons and tons of pictures for both the parent and the child. It is important for each of them to continue to feel like they know what is going on in one another's lives.