sample elasticsearch query to sort parent based on child field

gistfile1.txt

{  
  "query":{  
    "has_child":{  
      "query":{  
        "function_score":{  
          "functions":[  
            {  
              "field_value_factor":{  
                "factor":1,
                "field":"count"
              }
            }
          ]
        }
      },
      "score_mode":"avg",
      "type":"my_child_doc_type"
    }
  }
}