Per the Study in the States website, here are some important reminders about volunteering:
You cannot receive any form of taxable income from your volunteer activity.
If the volunteer position is one for which an employer would otherwise hire someone, you may work there only with all necessary employment authorization.
During summer break you are still considered to be an F-1 student, and you are expected to comply with the rules and regulations governing F-1 status during this time. If your internship is off campus or located in a different US city, we strongly suggest that you speak with our office. You may need approval for CPT or Pre-Completion OPT in order for your internship to be acceptable.
We advise that you speak with our office regarding any internship opportunity that you would like to pursue. Even unpaid internships could be deemed as employment by USCIS, so it is best to take the necessary precautions.
No. F-2 dependents are not permitted to accept employment in the US.