The "Where-clause" does not work in the Query Langauge.
You should use use the /*[@fieldName = "value"] to select the items, like this:
update set @#__Workflow state# = "--GUID of the DRAFT workflow state--" from //*[@@id='--GUID of the parent Item--']/*[@#__Workflow state# = "--GUID of the original DRAFT workflow state--"];
update set @#__Workflow state# = "--GUID of the APPROVED workflow state--" from //*[@@id='--GUID of the parent Item--']/*[@#__Workflow state# = "--GUID of the original APPROVED workflow state--"];