Вы должны использовать метод
+ (QB_NONNULL QBRequest *)objectsWithClassName:(QB_NONNULL NSString *)className
extendedRequest:(QB_NULLABLE NSMutableDictionary QB_GENERIC(NSString *, NSString *) *)extendedRequest
successBlock:(QB_NULLABLE void (^)(QBResponse *QB_NONNULL_S response, NSArray QB_GENERIC(QBCOCustomObject *) *QB_NULLABLE_S objects, QBResponsePage *QB_NULLABLE_S page))successBlock
errorBlock:(QB_NULLABLE QBRequestErrorBlock)errorBlock;
с extendedRequest как:
NSMutableDictionary *extendedRequest = [NSMutableDictionary dictionary];
[requestParameters setObject:parendID forKey:@"_parent_id"];