The two are linked. Having children is at least partly an economic choice. People have spent decades working against "teen moms" and "single parents" and "welfare queens". Everyone is very clear that you must not have children unless you can comfortably afford to do so. And not just now, that has to be enduring economic security across their childhood. Now, how many people can comfortably afford to do so?
Are the people who want others to have more children prepared to pay for it? To help make sure that enough housing and infrastructure is built for them?