It is extremely difficult jane and would require addional assessments by other professionals eg doctors, nurses, psychologists, to support the social work assessment. In my experience it is very rare to find emotional abuse in isolation from any other type of abuse. I don't know how often emotional harm is used as the only grounds for care proceedings, but I suspect not often as it is so difficult to prove. For that reason I don't expect parents would be prosecuted very often either, but I do think it makes sense for it to be possible.
I think in almost forty years as a social worker I have come across only one case of emotional harm in isolation and it was very distressing to see. However, it was a long time ago when cases were never taken to court on these grounds, and I don't think it would reach the threshold for care proccedings even today.
I wonder if any other social workers on here have had experience of this?