SELECT 
  category_id, 
  parent_id 
FROM 
  cscart_categories 
WHERE 
  parent_id IN(
    2842, 2650, 2651, 2652, 2844, 2843, 2850, 
    2849, 2848, 2847, 2846, 2845, 3172, 
    3228, 3229, 3230, 3231, 3232, 3233, 
    3234, 3235, 3236, 3237, 3238, 3424
  )

Query time 0.00022

JSON explain

{
  "query_block": {
    "select_id": 1,
    "table": {
      "table_name": "cscart_categories",
      "access_type": "range",
      "possible_keys": ["parent"],
      "key": "parent",
      "key_length": "3",
      "used_key_parts": ["parent_id"],
      "rows": 25,
      "filtered": 100,
      "index_condition": "cscart_categories.parent_id in (2842,2650,2651,2652,2844,2843,2850,2849,2848,2847,2846,2845,3172,3228,3229,3230,3231,3232,3233,3234,3235,3236,3237,3238,3424)"
    }
  }
}