actionscript 3 - GetChildByName is not working -

i having problem in getting child starling.current.nativestage - here code

var temp:image = starling.current.nativestage.getchildbyname("ball"+turn)as image; trace(temp.name);

the code "cannot access property or method of null object reference." making mistake or what?

help me please note*i m noob in starling

nativestage returns flash stage. these flash.display.displayobjects. cast starling.display.image via as image. return null.

so, mean native flash stage, or starling stage - starling.current.stage?

var temp:image = starling.current.stage.getchildbyname("ball"+turn)as image; trace(temp ? temp.name : "temp null");