Referencing the stage from a loaded swf

I am converting my website, which has a liquid interface, to as3 but I am still learning and I have a problem.

I have child.swf that I load dynamically into parent.swf. When I run that I get:

TypeError: Error #1009: Cannot access a property or method of a null object reference.
Through trial and error I found that the null object is the child.swf trying to reference the stage at several places such as stage.stageWidth. If I comment all of them out it runs error free, but it also doesn’t do anything. I have tried replacing the first ‘stage’ with other things such as ‘root.stageWidth’ but no dice.

I was also wonder how I can have a button in child.swf unload itself from the parent.swf?