Good question. But actually, from the Biblical point of view, the moment Adam sinned is when he died and that's when all his unborn children died too.
Trapped in a metaphor and nowhere out, eh? There is actual life and there is potential life. Adam had actual life (heart beating). Adam and Eve had no children UNTIL children were born.
Confusing a potential with an actual is sloppy thinking. Only actual children can be born and only actual children can die.
Children are the result of birth! You are imputing life to non-existent entities. There was a potential for mating with Eve. If and when each successful pregnancy came to term and birth resulted THEN and only then did they have children.
This "moment Adam sinned is when he died and when all his unborn children died too" is simply rhetorical nonsense.
You may as well look at a forest and think of it as potential toothpicks, paper bags and firewood and then declare that it IS all those by-products. Further, you can burn down a forest and that forest is gone taking with it the potential for making toothpicks, paper bags and firewood. However, the forest is GONE. Adam, after his sin, was walking around, eating, drinking and ready for bedtime foreplay for 930 years! You cannot have it both ways!