Although they may not be required to file, you may give them the option to file anyways.

It can sometimes be beneficial to file the tax return because (1) it starts the statute of limitations, (2) it can alert you if anybody filed a false tax return in your name (or prevent one from being filed) and (3) some agencies require a tax return as proof of income for certain benefits (such as Medicaid, FAFSA, etc.).

I usually send the client an email that says they are not required to file a tax return, but I also outline the reasons above, and let them decide if they want to pay you to file a tax return or not.