AddChild to a parent's element (from iframe)

I would like to add a child to an element like this:

myLayout.root.contentItems[ 0 ].addChild( newItemConfig );

But from a child (meaning from an iframe):

parent.myLayout.root.contentItems[ 0 ].addChild( newItemConfig );

I get a function undefined when I call 'addChild'. How can I do that?

BTW I'm trying to do that (http://ift.tt/1HlXHzy , look at JS code) from an iframe