[irrational]

Tie things like social security, healthcare in old age, etc. to how many kids a person has had. You only get full retirement benefits if you have had three children and raise them to adulthood. There are bonus levels for going above three children. Those who are infertile can adopt to meet their quota.

[kredd]

Only 17% of families up here in Canada have 3+ children. Yeah, that proposal will never fly. I wouldn’t even support it, because it doesn’t really make “having children” a benefit for currently living families.

[irrational]

Oh, I don't think something like this should actually be implemented, but OP was looking for ideas and this was the first one that came to mind.