[jjk166]

Child mortality rates are lower than they have ever been. They are basically zero in the developed world, and falling quickly throughout the developing world already. It's mostly a solved problem. Where it remains high, it's typically a symptom of other problems which prevent people from accessing adequate food and medicine. These circumstances almost always have their unique nuances that prevent them from being simply addressed by a single large effort, instead demanding a unique response informed by experience with the local conditions.

Adding a single healthy year of life to every American who lives to be over 70 would add about twice as many healthy person-years than reducing the US infant mortality rate to zero. Reducing the world infant mortality rate to zero would be equivalent to adding roughly two healthy years to the lifespans of those who make it over 70.