code: def get_page_children_dict(self, page_qs=None):
          
          children_dict = defaultdict(list)
          for page in page_qs or self.pages_for_display:
              children_dict[page.path[:-page.steplen]].append(page)
          return children_dict
docs: Returns a dictionary of lists, where the keys are 'path' values for
          pages, and the value is a list of children pages for that page.