When I work with new parents the issue of mortality always comes up. It is interesting how until we have children we rarely, if ever think about dying and once we have them we do. Some people become frightened by their own mortality, others fear that their children will die and some fear both.
The reality is that when/if/how we die or the fact that we will die has not changed at all. Having children triggers our reptilian brains and we want to protect our young. As there is no certainty to our futures, we as parents are challenged by this uncertainty and confuse it with a fear of mortality.