Tracing a Child object

Hi, I have a question about tracing a child object in AS3. I was following the book "Papervision3D Essentials" and I can't figure out how to trace out one of the line the book mention.

In the Nesting Example, the book mention that I just have to put the line trace(childSphere.sceneX) in the rendering method and I would be able to find the world location of the child sphere.

But after numerous tries, I still encounter the following error.
1120: Access of undefined property childSphere.

I believe this is the code the book mention.

override protected function onRenderTick(e:Event=null):void
{
parentSphere.localRotationY++;
trace(childSphere.sceneX)
super.onRenderTick();
}


Can someone help me out? And thanks in advance.