SELECT 
  category_id, 
  parent_id 
FROM 
  cscart_categories 
WHERE 
  parent_id IN(
    3515, 3516, 3517, 3518, 3520, 3519, 3521, 
    3522, 3659, 3660, 3508, 3507, 3551, 
    3559, 3509, 3510, 3511, 3512, 3513, 
    3514, 2361, 333, 2301, 2414, 3639, 3638, 
    3534, 3535, 3536, 3537, 3538, 3441, 
    3442, 3443, 3444, 220, 221, 11, 2316, 
    12, 222, 223, 224, 2290, 2296, 194, 13, 
    195, 14, 44, 3523, 3524, 3525, 3526, 
    3527, 3528, 3529, 3530, 3531, 3532, 
    3533, 3661, 3662, 3663, 3664, 3783, 
    3881, 3897, 3904
  )

Query time 0.00041

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": 69,
      "filtered": 100,
      "index_condition": "cscart_categories.parent_id in (3515,3516,3517,3518,3520,3519,3521,3522,3659,3660,3508,3507,3551,3559,3509,3510,3511,3512,3513,3514,2361,333,2301,2414,3639,3638,3534,3535,3536,3537,3538,3441,3442,3443,3444,220,221,11,2316,12,222,223,224,2290,2296,194,13,195,14,44,3523,3524,3525,3526,3527,3528,3529,3530,3531,3532,3533,3661,3662,3663,3664,3783,3881,3897,3904)"
    }
  }
}