code: def child_class(self, child):
          
          for prop, klassdef in self.c_children.values():
              if child == prop:
                  if isinstance(klassdef, list):
                      return klassdef[0]
                  else:
                      return klassdef
          return None
docs: Return the class a child element should be an instance of
  
          :param child: The name of the child element
          :return: The class