I have a series of letters between my father, uncle and their parents while they were all interned by the Japanese in Shanghai in different prison camps during WW2. These take the form of Red Cross letters and include talk of some very everyday life activities, such as schooling, swimming. However, there are a couple of Christmas cards printed by my grandfather in prison camp and sent to my grandmother and father.
The attached photo shows my father (right) carrying a food tray in the prison camp just after VJ day.