Smaller children mortality does not mean they will leave longer lives, nor they are (or will be) healthier.
It also probably means longer lives, as health in the first few years is predictive of this. Largely as indicated by discrepencies in mortality by wealth and race:
http://www.childtrends.org/?indicators=life-expectancy
If a child dies at 10 instead of 2, the population life expectancy at 0 will be greater, but from 10 - the same.
Heck, even if dies at 80 instead of 2, this does not say anything about health, just the fact some dangerous early-life condition was addressed.
Smaller children mortality does not mean they will leave longer lives, nor they are (or will be) healthier.