code: def add_child(self, child, modify=False):
          
          SceneGraph.add_child(self, child)
          self.notify()
          if modify:
              child._model_matrix_transform[:] = trans.inverse_matrix(self.model_matrix_global)
              child._normal_matrix_transform[:] = trans.inverse_matrix(self.normal_matrix_global)
docs: Adds an object as a child in the scene graph. With modify=True, model_matrix_transform gets change from identity and prevents the changes of the coordinates of the child