As of last year, nearly half of America’s middle-aged adults found themselves members, willing or not, of what’s been called “the sandwich generation,” so named because these people have a child below them and an aging parent above them. There are all sorts of theories about why families choose to bear as many (or as few) children as they do, but one suggestion is that parents tend to have more children so that there will be more people for them to rely on financially in their old age.