Tough situation and one, if you get involved further, you may get no thanks for. But that's not to say you shouldn't do anything.
Few situations have come up recently where I've had to go back to the adage that you can only judge yourself on what you believe is right regardless of others actions.
It might be worth reaching out to the family first to explain your concerns, give them a chance, however you'll never really know what the family dynamics are like. Otherwise it might be a report to the local authorities to take advice. It sounds like you just want to do the right thing and it won't settle right with you to just leave it.