title: get all child nodes from json
body: <p>I have the following json:  </p>
  
  <pre><code>    var source=[{'k':'01'},
                  {'k':'02', 'children': [
                      {'k':'05'},
                      {'k':'06', 'children': [
                          {'k':'ABC'},
                          {'k':'PQR'}
                      ]},
                      {'k':'07'}
                  ]},
                  {'k':'03'}];
  </code></pre>
  
  <p>I want to be able to specify a value for k and get back all of the children (and grandchildren and great-grandchildren, etc.).</p>
  
  <p>For instance if I provide <code>'02'</code>, I want to receive </p>
  
  <pre><code>            [
                {'k':'05'},
                {'k':'06'},
                {'k':'ABC'},
                {'k':'PQR'},  
                {'k':'07'}
              ]
  </code></pre>