What about the children? Do their wants/needs count?
I'm not a social worker but I am a teacher and know only too well how parents can screw up their children. These other children are probably well into their teens now and will have so many questions for a parent who let them all down do badly. The desire for contact may well have come from those other children. And even if it's the mother who is requesting contact, the decision to allow it may well have been made (by people who know all the facts) for the benefit of those children. If limited and supervised contact will help those children get answers to the many questions they have, and therefore help them move on with their lives, is it such a bad thing?
There's always a big picture.