I think finances are more a concern/incentive.

Consider: the government pays a salary to each married family while they raise children; the salary would be equivalent to a blue-collar job, and it would scale with the number of children up to a point (e.g. 4 kids).

I strongly believe that'd lead to many more marriages and childbirths. Many people not interested in raising kids would prefer it over a "regular" job. Families with adoptive children would also be paid, so it could decrease adoption difficulty and stigma as a side-effect.

However, some people will game this policy, and it would be very expensive to implement.