recursive_yield_example.rb

require 'json'
class MyJsonHierarchyReader

  # @param [#each] input_stream Probably a file, but any iterator will do
  # so long as it returns a valid JSON object from #each
  def initialize(input_stream, settings)
    # ... whatever you need to do. Let's pretend it's
    # a newline-delimited JSON file, since you didn't
    # specify anything
    @json_lines = input_stream
  end

  def each(&blk)
    @json_lines.each do |jline|
      h = JSON.parse jline
      recursive_yield(h, blk)
    end
  end

  def recursive_yield(h, blk)
    doc = build_a_doc(h)
    blk.call doc
    Array(h['children']).each do |child|
      recursive_yield(child, blk)
    end
  end

  def build_a_doc(h)
    {"my_id" => h['id'] }
  end

end

sample_record1 = {
    id:       1,
    children: [
       { id: 2,
         children: [
           { id: 3 },
           { id: 4 }
         ]
       },
       {id: 5,
        children: [
            {id: 6},
            {id: 7}
            ]
       }
    ]
}

sample_record2 = {
    id:       10,
    children: [
                  { id: 20,
                    children: [
                            { id: 30 },
                            { id: 40 }
                        ]
                  },
                  {id: 50,
                   children: [
                           {id: 60},
                           {id: 70}
                       ]
                  }
              ]
}

records = [sample_record1.to_json, sample_record2.to_json]

require 'pp'
reader  = MyJsonHierarchyReader.new(records, {})
reader.each {|doc| pp doc }

Output is what you'd expect:

{"my_id"=>1}
{"my_id"=>2}
{"my_id"=>3}
{"my_id"=>4}
{"my_id"=>5}
{"my_id"=>6}
{"my_id"=>7}
{"my_id"=>10}
{"my_id"=>20}
{"my_id"=>30}
{"my_id"=>40}
{"my_id"=>50}
{"my_id"=>60}
{"my_id"=>70}