In any situation where you have to make decisions based on unknown information (in this case, what the child's life would be like with their mother), you will have false positives and false negatives.
I.e., sometimes children will be taken away who should have been left with their mum. And sometimes children will be left with their mum who should have been taken away (most famously Baby P.)
When you're designing protocols, you have to decide which way you'd rather err. Would you rather take no chances and risk putting some children into care who might have done all right at home? Or would you rather take more chances and risk more children ending up victims of neglect and abuse?
In this country we have the Children's Act, which means that the best interests of the child come before the interests of the parent. We have also decided as a nation that we don't want any more children to end up like Baby P. That means that, yes, social services take more children into care than they used to (care proceedings are up by 130% in the last ten years). But that's because we think false negatives (Baby Ps) are more important than false positives (borderline parents who might well have ended up doing okay.)