ParentDataValue is some common data value between the parent and the child (e.g. company name)
ParentLink is the unique identifier you mention.
ChildDataValue is a sortable datavalue for the child docs (e.g. PersonLastName)
With this scheme, your view is sorted on a viewable data value and quick search still works! Since the parent doc does not have a ChildDataValue, it floats to the top of the group.