This “can’t afford children” is often an illusion, especially since you mention the tax rate that improves with more dependents. I am in California too and I see 6-8-kid families filling entire pews in church. They are single provider families that often struggle to pay bills, but they are not on welfare. It is a choice: you drive an older car, the kids learn to go without expensive clothes, take care of the little siblings, and share rooms, and are better off for it.
Everyone I know who “can’t afford more children” has a more expensive house than my family’s. It’s simply a matter of prioritizing.