My thanks to Frances, Liz, Mary & Sue. I do indeed have the exact ages at death and burial dates; Mike Calder from the IOM "Lookup" List sent me this information some time ago, and as well I have a Certificate of Burial for the mother (3 Jan 1877), however, the causes of their deaths is not mentioned.

As Frances has indicated, even a relatively minor (by today's standards) disease, but combined with perhaps under-nourished children, could well have been the reason. I will be content with the assumption that generally poor health and living conditions played a part in the deaths.

My thanks once again for all your input.