Child targeting Parent - AS3

Would someone please help me to correctly get a LOADED SWF to target a LOADER SWF?

I have a button in the LOADED SWF that “addChild” to the LOADER SWF.

I have the following action in the LOADED SWF:

stage.root.parent.addChild(button_btn);

It doesn’t work and the error message is: “Access of undefined property button_btn”

Any help would be deeply appreciated!!