SELECT 
  category_id, 
  parent_id 
FROM 
  cscart_categories 
WHERE 
  parent_id IN(
    1277, 1278, 1279, 1283, 1284, 1274, 1280, 
    1285, 1276, 1282, 1281, 1275
  ) 
  AND category_id != 265

Query time 0.00045

JSON explain

{
  "query_block": {
    "select_id": 1,
    "table": {
      "table_name": "cscart_categories",
      "access_type": "range",
      "possible_keys": ["PRIMARY", "parent", "p_category_id"],
      "key": "parent",
      "key_length": "3",
      "used_key_parts": ["parent_id"],
      "rows": 15,
      "filtered": 100,
      "index_condition": "cscart_categories.parent_id in (1277,1278,1279,1283,1284,1274,1280,1285,1276,1282,1281,1275)",
      "attached_condition": "cscart_categories.category_id <> 265"
    }
  }
}