PUT my_index
{
  "mappings": {
    "my_parent": {},
    "my_child": {
      "_parent": {
        "type": "my_parent"
      }
    }
  }
}

PUT my_index/my_parent/1
{
  "text": "This is a parent document"
}

PUT my_index/my_child/2?parent=1
{
  "text": "This is a child document"
}

PUT my_index/my_child/3?parent=1&refresh=true
{
  "text": "This is another child document"
}

GET my_index/my_parent/_search
{
  "query": {
    "has_child": {
      "type": "my_child",
      "query": {
        "match": {
          "text": "child document"
        }
      }
    }
  }
}

GET my_index/my_child/_search
{
  "query": {
    "has_parent": {
      "parent_type": "my_parent",
      "query": {
        "match": {
          "text": "parent"
        }
      }
    }
  }
}