If you have any suspicions whatsoever you need to speak out, certainly not to the parents though. They'll probably go ape at you for questioning their parenting skills and i certainly wouldn't want to get on the wrong side of the mother, she sounds derailed. As others have quite rightly suggested i think the anonymous route is the wise one to take, but you must say something to the authorities, you can't let this ride and hope it gets better. If an ambulance pulls up one morning taking one of the kids to the hospital you'd feel like crap.