What would you do if you were too poor to care for your children? If you said have less children, you have not factored in the economics of welfare:
The 1996 Personal Responsibility and Work Opportunity Reconciliation Act (PRWORA) gave states greater flexibility to formulate and implement initiatives to reduce welfare dependency and encourage employment for members of low-income families with children. For the nation, in 2006, 10 years after passage of the Act, the birth rate for women 15 to 50 years old receiving public assistance income in the last 12 months was 155 births per 1,000 women, about three times the rate for women not receiving public assistance (53 births per 1,000 women).
In other words, when you subsidize children, you create the incentive to have more children…3x the national average, in this case. Link via Perry here.