<human>: Can you succinctly summarize the text in 1-3 sentences?

I teach art lessons to underprivileged youths at a nearby elementary school through an organization at my university.  After only ever teaching in middle/upper class areas, working with these kids has been a very eye-opening experience.  I'll cut to the chase though... Today was my last day working with this particular class of kids, and one table started talking about when they were afraid of their parents.  Two girls admitted that their parents regularly belted them, with one also saying her dad whipped her with metal wire, too, and the other saying her dad pounded her hand with a brick.  When I tried to tell them that it was wrong for their parents to hurt them and told them it's illegal, they disagreed and thought it wasn't illegal.  Yet another started crying when she got a somewhat poor progress report she had to take home for her parents to sign, saying her dad was going to beat her like he usually did.  A different girl also told me that her mom calls her a "fat bitch" and that her dad was deported and went to jail after trying to kill her mother.

I asked the graduate student who serves as supervisor of the other undergraduate mentors like me what, if anything, I should do.  Her exact words were, "If you didn't see bruises, you can't say shit."  In a sad way I agree, and I realize I also have no proof that these kids are telling the truth, although they seemed serious.  But thinking about some man taking a brick to a 9 year-old girl just makes me sick.

So I thought I'd ask you, Reddit.  What can or should I do?  I need some peace of mind.

Some background notes: I am a 20 year-old white female in California.  My kids are 5th graders, primarily Hispanic, and low income.  I am not an official teacher or counselor-- just a college volunteer mentor.
<bot>: Have heard MULTIPLE testaments from my 5th grade mentees that their parents abuse them.  What can I realistically do? (that won't just be a bunch of useless paperwork that angers the parents more)