Children have become more of a burden than a benefit in many ways. We once had much use for our children. When people were more independent and everyone pretty much had a small business, children were seen as the life blood of that business. Now, we are pretty much expected to fill a role at some large corporation -- which Japan is the greatest example of. Also, the family centered culture has changed to a work cente…
Pre-modern agricultural societies had huge families because there was so much work that you could always use an extra pair of hands. (Also, many of them died off anyway so you had to factor that in.) You are looking at the past with a seriously rose-tinted lens.