ACTC for expats

My wife and I live with our 4 children all under 16 outside of the US. We are all US citizens. We have no tax liability in the US. I believe that we still qualify for the ACTC (last year we paid a CPA to do out taxes, we were in the same situation, and we received the ACTC). TT says "since the Additional Child Tax Credit is a refundable credit, but your tax return did not show any earned income, you did not meet that credit's $2,500 minimum earned income requirement." Of course, we have income that is reported, it just is not taxable. How do I get around this?