Jquery json building

[sunny]

http://jsfiddle.net/hot0Lg5v/  in my fiddle there is a json how can i send the key value
This is drag and drop model when you drag json is created open the console and see the json i want to send the key

that's json when you drop two modules

{"children":[{"data":{"id":"213","timeout":"20","can_call_self":false},"key":"","module":"device","children":[{"data":{"id":123,"timeout":12,"can_call_self":false},"key":"","module":"user","children":[]}]}]}
this is  i want

{"children":[{"data":{"id":"213","timeout":"20","can_call_self":false},"key":"_","module":"device","children":[{"data":{"id":123,"timeout":12,"can_call_self":false},"key":"1","module":"user","children":[]}]}]}