How do you assign a child datagrid which have more than one parent?

When you have a parent and child datagrid pair, you can assign the child
datagrid using:

DataSet11.Relations.Add("ParentChildRelationshipNa me", _
DataSet11.Tables("ParentTable").Columns("FieldName "), _
DataSet11.Tables("ChildTable").Columns("FieldName" ))

DataGrid2.DataSource = DataSet11
DataGrid2.DataMember = "ParentTable.ParentChildRelationshipName"

BUT, now I have multiple parent datagrids, each with a relationship to one
child table. How do I set the DATAMEMBER property then?