Yes, it is for any Child Tax Credit.

When the law was first passed, I thought it was just the refundable part too, but it is for any of it (including the new 2018 $500 partial credit for 'other' dependents).

Section 6695(g)(2) requires Due Diligence on "the credit allowable by section 24, 25A(a)(1), or 32". Section 24 is the Child Tax Credit. See also 1.6695-2 and 1.6695-2T.