Looking through the various new tax calculators. Due to the new standard deduction for married filing jointly, taxable income doesn't even begin until $24,001. If that couple has the standard 2 kids, they will have $0 tax liability up to a net income of $60,500 due to the standard deduction and the increased child credit. Tax liability at $60,500 is $3,999 and is offest by $4,000 child credit.
Under existing, that same married couple with 2 kids with $60,500 in income has a tax liability of $3,022. Under existing, a tax liability occurs down to $40,350.
Here's one up to date one I messed with. It has a link to their 2017 calculator.
https://www.calcxml.com/calculators/trump-tax-reform-calculator
When I get home I'll post a link to one calculator I found that compares new and existing and I believe it also includes the fully refundable part of the child tax credit as well. That gives parents below the threshold of tax liability up to $1,400 additional in their refund.