code: private void deletePolymorphicChildrenShallow(OneToManyPolymorphicAssociation association){
          String targetTable = metaModelOf(association.getTargetClass()).getTableName();
          String parentType = association.getTypeLabel();
          new DB(metaModelLocal.getDbName()).exec("DELETE FROM " + targetTable + " WHERE parent_id = ? AND parent_type = ?", getId(), parentType);
      }
docs: Deletes immediate polymorphic children