It's pretty well documented and accepted that most abusers were once victims themselves. Does that mean that anyone who was on the "at risk" file as a child should expect their children to be added to the same list automatically.
These crimes against children are horrifying and despicable and no amount of exposure to this sort of thing can de-sensitise you to it, but the answer is not obvious.
Regular checks by health visitors to all families, whatever their background, should pick up on some of the worst cases but health visitors, like any parent, knows that children DO fall over and pick up bruises no matter how good your parenting skills are and it's often difficult to spot a child at risk.
This doesn't excuse those who didn't follow up on the welfare of the child in this case whose claims that they were too afraid of the parents is quite shocking.
I imagine those people will be suffering in their own way now.