SELECT 
  category_id 
FROM 
  cscart_categories 
WHERE 
  parent_id = 34 
  AND status = 'A' 
ORDER BY 
  position

Query time 0.00159

JSON explain

{
  "query_block": {
    "select_id": 1,
    "read_sorted_file": {
      "filesort": {
        "sort_key": "cscart_categories.position",
        "table": {
          "table_name": "cscart_categories",
          "access_type": "ref",
          "possible_keys": ["parent"],
          "key": "parent",
          "key_length": "3",
          "used_key_parts": ["parent_id"],
          "ref": ["const"],
          "rows": 5,
          "filtered": 100,
          "attached_condition": "cscart_categories.parent_id <=> 34 and cscart_categories.`status` = 'A'"
        }
      }
    }
  }
}