SELECT 
  category_id, 
  parent_id 
FROM 
  cscart_categories 
WHERE 
  parent_id IN(434)

Query time 0.00024

Explain
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE cscart_categories ref parent parent 3 const 5

Result

category_id parent_id
442 434
454 434
463 434
474 434
477 434