There have always been children living in isolated rural communities. Always. Japan is in no way special in this regard, nor is it special in having a low birth rate nor in it having a declining population. South Korea, for example, has a lower total fertility rate than Japan. But people love to focus on Japan and project their own values and beliefs on it, values which are not necessarily shared by the Japanese people, many of whom feel that their nation's population grew too large.
No, Japan is unique in this regard. Yes, South Korea, China and much of Europe is following along the same trend lines, but Japan is good couple of decades ahead of everybody else and is thus the world's guinea pig for population decline:
The lines are the country's % of working-age people. As you can see, Japan is already collapsing rapidly, while South Korea is just starting to plateau out and China is still climbing.
There have always been children living in isolated rural communities. Always. Japan is in no way special in this regard, nor is it special in having a low birth rate nor in it having a declining population. South Korea, for example, has a lower total fertility rate than Japan. But people love to focus on Japan and project their own values and beliefs on it, values which are not necessarily shared by the Japanese people, many of whom feel that their nation's population grew too large.