Have you seen those Hallmark type books that are voice recorded? You can get them from newsagents. If you cant find one I will get one and send it you. It is really great as you can get DP to read the story while recording it and then it can be DS's special book when he misses daddy and he can press the buttons for each page to hear daddy read him the story.

I would also do things for Daddy when he misses him. Maybe a painting and then you can take it in to DP (as I am sure it would lift his spirits while away from DS as well).

Maybe some of the ladies who have Dp's/Dh's in the army might have some other suggestions as they may be away from their children for long periods of time.