opping back a few years to when the war had only been going on for a few weeks, this card displays a pleasant, and for the time, essential, sense of humour.
I can only assume that "My co-digger and I" refers to the fact that the sender is busy installing an air-raid shelter in preparation for the coming onslaught. At that early stage of the war - known as the "Phoney War", due to the fact that from a British citizens' point of view there was little apparent action - none of the people digging their shelters in could have possibly realised what hardships they would soon be enduring.
I wonder if the five "poor Coventry Evacuees" stayed at their safe-homes for long? Relatively few people took up the evacuation option, and in the early part of the war, many returned after quite a short while, for the same reason as given above.