In the populate List From Array behavior that is applied to the Parent list, you are using the rsChild Dynamic Array (rsChild_WAJA):
<select name="parent" size="10" onchange="WA_FilterAndPopulateSubList(rsChild_WAJA,MM_findObj('parent'),MM_findObj('child'),0,0,false,': ')">
Again, you use that same dynamic array in the Populate List from Array behavior that is applied to the Child List (rsChild_WAJA):
<select name="child" size="10" onchange="WA_FilterAndPopulateSubList(rsChild_WAJA,MM_findObj('child'),MM_findObj('target'),0,0,false,': ')">
to use the rsGchild array, that code should be:
<select name="child" size="10" onchange="WA_FilterAndPopulateSubList(rsGchild_WAJA,MM_findObj('child'),MM_findObj('target'),0,0,false,': ')">