SELECT 
  category_id, 
  parent_id 
FROM 
  cscart_categories 
WHERE 
  parent_id IN(605, 606, 607, 608, 609, 610) 
  AND category_id != 264

Query time 0.00034

Explain
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE cscart_categories range PRIMARY,parent,p_category_id parent 3 9 Using index condition; Using where

Result

category_id parent_id
611 610
612 610
613 610
614 610
615 610