More precisely, it seems to be to improve the strength of social safety nets (that correlates with standard of living, but also explains places in the developed world where the average standard of living is high by developed world standards but the birthrate is also high for the developed world.)

The reason for this may be that, in the absence of public social safety net, family (and particularly close family) serve as a safety net, and particularly children, once they are able to be productive, can be a kind of safety net against infirmity for their parents.