To be fair, truly low income families generally do not pay taxes as is. So tax credits do nothing for them. These policies have the most impact on middle class families, who can afford to have 1-2 kids and are certainly free (but should not be encouraged) to have more. I would, however, be in favor of a substantial adoption tax credit.
I think you are confusing tax deductions with credits. Deductions reduce your taxable income, and therefore have less benefit to no benefit for people with income that's already below the standard deduction. Many tax credits are "refundable", meaning the gov pays you the credit whether you have any taxable income or not, as long as you file a return. So many tax credits are a huge subsidy to poors - especially the child tax credit. Granted, there are also tax credits for rich people stuff the poors could never afford, like electric cars.
I would much prefer tax reform that replaces credits with more generous deductions.