SELECT 
  parent_id, 
  COUNT(page_id) as children 
FROM 
  cscart_pages 
  INNER JOIN cscart_ult_objects_sharing ON (
    cscart_ult_objects_sharing.share_object_id = cscart_pages.page_id 
    AND cscart_ult_objects_sharing.share_company_id = 1 
    AND cscart_ult_objects_sharing.share_object_type = 'pages'
  ) 
WHERE 
  parent_id IN (
    54, 106, 66, 42, 108, 15, 79, 16, 21, 62, 
    56, 50, 53, 52, 51, 38, 47, 48, 49, 78, 
    31, 43, 27, 12, 63, 65, 77, 73, 45, 44, 
    23, 25, 22, 20, 19, 26, 28, 40, 41, 109, 
    32, 34, 33, 103
  ) 
GROUP BY 
  parent_id

Query time 0.01344

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "34.67"
    },
    "grouping_operation": {
      "using_temporary_table": true,
      "using_filesort": true,
      "cost_info": {
        "sort_cost": "1.21"
      },
      "nested_loop": [
        {
          "table": {
            "table_name": "cscart_ult_objects_sharing",
            "access_type": "index",
            "possible_keys": [
              "PRIMARY"
            ],
            "key": "PRIMARY",
            "used_key_parts": [
              "share_object_id",
              "share_company_id",
              "share_object_type"
            ],
            "key_length": "159",
            "rows_examined_per_scan": 144,
            "rows_produced_per_join": 1,
            "filtered": "1.00",
            "using_index": true,
            "cost_info": {
              "read_cost": "31.45",
              "eval_cost": "0.29",
              "prefix_cost": "31.73",
              "data_read_per_join": "230"
            },
            "used_columns": [
              "share_company_id",
              "share_object_id",
              "share_object_type"
            ],
            "attached_condition": "((`ea201_diorama`.`cscart_ult_objects_sharing`.`share_company_id` = 1) and (`ea201_diorama`.`cscart_ult_objects_sharing`.`share_object_type` = 'pages'))"
          }
        },
        {
          "table": {
            "table_name": "cscart_pages",
            "access_type": "eq_ref",
            "possible_keys": [
              "PRIMARY",
              "parent_id"
            ],
            "key": "PRIMARY",
            "used_key_parts": [
              "page_id"
            ],
            "key_length": "3",
            "ref": [
              "ea201_diorama.cscart_ult_objects_sharing.share_object_id"
            ],
            "rows_examined_per_scan": 1,
            "rows_produced_per_join": 1,
            "filtered": "84.21",
            "index_condition": "(`ea201_diorama`.`cscart_ult_objects_sharing`.`share_object_id` = `ea201_diorama`.`cscart_pages`.`page_id`)",
            "cost_info": {
              "read_cost": "1.44",
              "eval_cost": "0.24",
              "prefix_cost": "33.46",
              "data_read_per_join": "2K"
            },
            "used_columns": [
              "page_id",
              "parent_id"
            ],
            "attached_condition": "(`ea201_diorama`.`cscart_pages`.`parent_id` in (54,106,66,42,108,15,79,16,21,62,56,50,53,52,51,38,47,48,49,78,31,43,27,12,63,65,77,73,45,44,23,25,22,20,19,26,28,40,41,109,32,34,33,103))"
          }
        }
      ]
    }
  }
}