In the US, it's a $2,000 tax credit per kid, so you effectively only get paid if your household income is high enough to owe federal income tax, and low enough

In the US, it's a $2,000 tax credit per kid, so you effectively only get paid if your household income is high enough to owe federal income tax, and low enough that the 5% phase-out doesn't eat up the whole benefit. Also, it comes off of your taxable income, so the net benefit to your pocket is (1.0 - marginal_tax_rate) * benefit.