At certain historic moments, grandparents took on childrearing responsibilities. In many cultures, they still do. Chinese grandparents who are able to retire at 55 are seen all over Beijing bouncing grandbabies. In the United States, we can't afford to retire at 55.
“A man's felicity consists not in the outward and visible blessing of fortune, but in the inward and unseen perfections and riches of the mind.”