My parents brought me to the U.S. from Mexico when I was a child, and I'm a student here, who has applied for and been granted Deferred Action for Childhood Arrivals (DACA). However, I haven't seen my grandparents or various other relations in years, and would really like to go back and visit them. I hear that if I get something called "advance parole," I can travel outside the U.S. and be let back in. Will this really work?
It's possible you might be granted Advance Parole, but this depends on facts beyond what you've given here. The rule is that U.S. Citizenship and Immigration Services (USCIS) may grant this status to a DACA applicant if the trip is for purposes to do with education, employment, or urgent humanitarian reasons. The agency will not grant Advance Parole for a mere vacation.
From what you've described, your reasons for wanting to leave have nothing to do with education or employment. The closest possibility for you is "urgent humanitarian" reasons, but the question is, how urgent is your situation?
The examples USCIS gives in its Instructions for Form I-131 (the form used to apply for Advance Parole) include "to obtain medical treatment, attend funeral services for a family member, or visit an ailing relative." If you don't fit into one of these categories, it's possible USCIS will view your planned trip as a vacation.
The cruel truth of the matter is that if all your family members are in good health, you might have a tough time obtaining Advance Parole. Then again, USCIS policy under the Trump Administration was especially harsh; it might soften under the Biden Administration.
In any case, if a member of your family is quite ill, or there exists a similarly sympathetic situation warranting your return, this will strengthen your case. You would definitely want to obtain documentation of this fact, such as medical test results and a recent doctor's letter emphasizing the seriousness of the person's condition and the importance of your visit, and include these with your Advance Parole application.
For more information on the application process, see DACA Recipients: How to Apply for a Travel Document (Advance Parole).
If USCIS does grant you Advance Parole, it will give you a form called an I-512L, which you can show to the U.S. border officers upon your return.
Realize, however, that the I-512L is not an absolute guarantee that you will be allowed to return to the United States—though you certainly should not leave the U.S. without it. An experienced immigration attorney can prepare the paperwork for you and assess your level of risk upon return.