Some demography experts mention that financial incentives do work starting from the second child (if provided as a lump sum, and with usage not restricted too much). It's not something that can stop the population decline, but it can slow it down to some extent.

https://www.econstor.eu/bitstream/10419/216331/1/dp13019.pdf

The rest, statistically speaking, doesn't make much of a dent in the established social and religious conventions of any given nation, which the governments generally have little control of.