grandchildren

my 2 grandchildren were recently taken off their mother (my sons ex)for beating up my 7 year old grandson amongst other things, and put in the care of my son. the court case is due shortly for my son to go for residecy order, the mother had a drugs test which came back positive stating very high doses of amphetamines, cannabis, and ecstasy drug 3,4.
the children see thier mother three afternoons a week but the social services are happy for her to keep her other child of 1 year old, not my sons under the same roof can anyone tell me if this is the right procedure as our family are worried over this child although we have never met her.
thank you wayne2000