"Child Mortality Impact: Lower overall averages compared to modern times stem largely from higher rates of infant and childhood mortality during this"

That was a lot of it till about 50-100 years ago. Lots of infant deaths in a local cemetery back 100 years ago and more. There were lots of people living to ripe old ages once they got past childhood. Modern medicine keeps old codgers like myself alive beyond when they should be sometimes but it is offset by poor diet and lifestyles mostly.