Multiple swf communication

how do I get my child swf to communicate with my main swf?

(this is main1.swf)

var homeRequest:URLRequest = new URLRequest(“window1.swf”);
var homeLoader:Loader = new Loader();
homeLoader.load(homeRequest);
addChild(homeLoader);

loads in the child swf

I want the child to call a function that exists on the main swf

(this is window1.swf)

stop();
myBtn.addEventListener(MouseEvent.CLICK, testThis);

function testThis(event:MouseEvent):void {
MovieClip(root).activatemyfunction();
trace(“you have clicked this”)
}

Obviously, MovieClip(root) is not getting to the main.swf’s root timeline. What code do I need to do this?