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 (
    86, 87, 91, 32, 83, 9, 16, 85, 17, 19, 48, 
    65, 77, 20, 90, 31, 88, 18, 78, 47, 89, 
    26, 73, 8, 80, 34, 84, 81, 64, 79, 42, 11, 
    3, 4, 5, 71, 75
  ) 
GROUP BY 
  parent_id

Query time 0.00062

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "44.69"
    },
    "grouping_operation": {
      "using_temporary_table": true,
      "using_filesort": true,
      "cost_info": {
        "sort_cost": "1.12"
      },
      "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": 191,
            "rows_produced_per_join": 1,
            "filtered": "1.00",
            "using_index": true,
            "cost_info": {
              "read_cost": "40.90",
              "eval_cost": "0.38",
              "prefix_cost": "41.28",
              "data_read_per_join": "305"
            },
            "used_columns": [
              "share_company_id",
              "share_object_id",
              "share_object_type"
            ],
            "attached_condition": "((`ea201_francemaqu`.`cscart_ult_objects_sharing`.`share_company_id` = 1) and (`ea201_francemaqu`.`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_francemaqu.cscart_ult_objects_sharing.share_object_id"
            ],
            "rows_examined_per_scan": 1,
            "rows_produced_per_join": 1,
            "filtered": "58.73",
            "index_condition": "(`ea201_francemaqu`.`cscart_ult_objects_sharing`.`share_object_id` = `ea201_francemaqu`.`cscart_pages`.`page_id`)",
            "cost_info": {
              "read_cost": "1.91",
              "eval_cost": "0.22",
              "prefix_cost": "43.57",
              "data_read_per_join": "2K"
            },
            "used_columns": [
              "page_id",
              "parent_id"
            ],
            "attached_condition": "(`ea201_francemaqu`.`cscart_pages`.`parent_id` in (86,87,91,32,83,9,16,85,17,19,48,65,77,20,90,31,88,18,78,47,89,26,73,8,80,34,84,81,64,79,42,11,3,4,5,71,75))"
          }
        }
      ]
    }
  }
}