… is from page 64 of Angus Deaton’s excellent 2013 book, The Great Escape:
Saving the lives of children has a bigger effect on life expectancy than saving the lives of the elderly. A newborn who might have died but does not has the chance to live many more years, which is not the case when a 70-year-old is pulled through a life-threatening crisis. This is also one of the reasons why the rate of increase in life expectancy has slowed down in recent years; mortality among children is now so low that progress can only really take place among older adults, among whom reductions in mortality rates have smaller effects on life expectancy.