I've used a writ of habeas corpus (Latin for "Produce The Body") in a child abduction case involving a jealous sister. If the Massachusetts social workers step over the line, and it looks like they have, they can be hauled into federal court with a habeas corpus writ to return the children to their parents. Furthermore, since state action was involved, the State would have to pay the parents' attorney fees for violating their civil rights and those of their children.
The idjits took the kids away from their parents when the kids refused to obey the idjits. That's a constitutional due process violation.