yii\rbac\DbManager::removeChildren PHP Method

    public function removeChildren($parent)
    {
        $result = $this->db->createCommand()->delete($this->itemChildTable, ['parent' => $parent->name])->execute() > 0;
        $this->invalidateCache();
        return $result;
    }

 /**
  * Update role using string name.
  *
  * @param string $id
  * @return mixed
  * @throws NotFoundHttpException
  */
 public function actionUpdate($id)
 {
     $this->layout = '@app/views/layouts/one-column';
     $role = $this->findRole($id);
     $model = RoleForm::createFromRole($role, $this->authManager->getChildren($role->name));
     /* @var $systemAlert Alert */
     $systemAlert = Yii::$app->systemAlert;
     if (Yii::$app->request->isAjax && $model->load($_POST)) {
         Yii::$app->response->format = Response::FORMAT_JSON;
         return ActiveForm::validate($model);
     }
     if ($model->load($_POST) && $model->validate()) {
         $transaction = Yii::$app->db->beginTransaction();
         try {
             // update role description
             $role->description = $model->description;
             if (!$this->authManager->update($role->name, $role)) {
                 throw new Exception();
             }
             // update role permissions
             $this->authManager->removeChildren($role);
             foreach ($model->getPermissionModels() as $permission) {
                 $this->authManager->addChild($role, $permission);
             }
             $transaction->commit();
             $systemAlert->setMessage(Alert::SUCCESS, Yii::t('user', 'Role updated successfully'));
             return $this->redirect(['index']);
         } catch (Exception $ex) {
             $transaction->rollback();
             $systemAlert->setMessage(Alert::DANGER, Yii::t('app', 'System error: {message}', ['message' => $ex->getMessage()]));
         }
     }
     return $this->render('update', ['model' => $model]);
 }