Perhaps there is no word for it because childhood death was so much more expected than other deaths.

This may get to the nub of the matter better than my somewhat glib suggestion. Also being a widow, widower or orphan made a significant difference in one's life style. When a woman was economically dependent on having a man in her life and a man was just as dependent, for other reasons, in having a woman in his, noting that one was without the husband or wife was an important consideration. For a child to have no parents is still an important consideration. If all of one's children have died and the woman is past the age for bearing more, then there is only the matter of inheritance, and I'm sure there's a legal term for that.