What @puravidapto explained is not exactly correct.

Your client will not, prima facie, be eligible for CTC in the first place because TCJA amended §24 to disallow, up to TY2025, the credit unless the qualifying child was issued an SSN as a US citizen, green card holder, or as a resident alien with employment authorization, pursuant to §24(h)(7).

The test that is used to determine the tax residency status of an individual under §7701 is substantial presence test (not to be confused with physical presence test as defined under §911 for purposes of foreign earned income exclusion).

As with many tax provisions, there are exceptions and visa type does make a difference - for example, certain individuals who hold certain types of visas such as F, J, and Q are exempted from counting certain US days of presence for purposes of substantial presence test.  Unless your client was previously an exempt individual, this would apparently not apply in your client's case.