You should check what that number on the W-2 is because it will affect the credit he may get for the withholding.  Unless you know for sure why there is that series of numbers and what it is, you can't really file his return or apply for an ITIN.

It is correct he is not eligible for CTC (not withstanding other requirements) if he doesn't have an ITIN issued on or before the due date for filing his return.  This is codified under §24(e)(2).