SELECT 
  category_id, 
  parent_id 
FROM 
  cscart_categories 
WHERE 
  parent_id IN(
    280, 271, 264, 276, 281, 272, 265, 266, 
    273, 274, 267, 268, 275, 269, 270
  )

Query time 0.00027

JSON explain

{
  "query_block": {
    "select_id": 1,
    "nested_loop": [
      {
        "table": {
          "table_name": "cscart_categories",
          "access_type": "ALL",
          "possible_keys": ["parent"],
          "rows": 18,
          "filtered": 100,
          "attached_condition": "cscart_categories.parent_id in (280,271,264,276,281,272,265,266,273,274,267,268,275,269,270)"
        }
      }
    ]
  }
}