Thanks a lot. It looks like in the case I was asking for, although I can claim them as dependents, there is no exception regarding the tax credit. I went through the links you provided and the [instructions for the form 1040](<a rel="nofollow" target="_blank" href="https://www.irs.gov/pub/irs-pdf/i1040gi.pdf">https://www.irs.gov/pub/irs-pdf/i1040gi.pdf</a>). I think you could add some details to your answer to make it a bit more complete:

Yes, they can be residents of Mexico or Canada and still qualify as a "Qualifying Relative", but a being a "Qualifying Relative" only means that you can claim them as dependents, but not necessarily that they will qualify for the tax credit.

For them to be your "Qualifying Relative", you need to meet the income and support conditions and, they need to live with you or meet the exceptions for (close relatives)[<a rel="nofollow" target="_blank" href="https://www.irs.gov/publications/p17">https://www.irs.gov/publications/p17</a>] like your parent, grandparent, sibling, niece or nephew.

For them to qualify for the tax credit they also have to be a  U.S. citizen, U.S. resident alien, or U.S. national.

For additional information see [What is the $500 Credit for Other Dependents (“Family Tax Credit”)?](<a rel="nofollow" target="_blank" href="https://ttlc.intuit.com/questions/4499708-what-is-the-500-credit-for-other-dependents-family-tax-cre...>)