IRS Reduced My Return by $2000, citing child tax credit on line 52

As far as I know, all of my forms should be correct, since I let TurboTax fill them. I'm having trouble chasing down this problem. Relevant details:

• We have two, adopted kids, under 17.
• Turbotax shows a $4k federal return.
• There's a zero in 1040 line 52.

Could TurboTax have made a mistake, could I have confused it, or should I follow up with the IRS?

Since it's $2,000, I thought it might be worth checking into. 🙂

Thanks