Can't get "getChildIndex" button setup to get index's of button's

Hi,

I have put 6 movieclips that I’m using as buttons on stage… each button should be driven by this class:

package {
	import flash.display.*;
	import flash.events.*
	import SceneNavigation;
	//import caurina.transitions.properties.FilterShortcuts;

	public class ButtonSetup extends MovieClip {
		
		private var siteNav:SceneNavigation = new SceneNavigation();
		private var whichBtn:Number;

		public function ButtonSetup() {
			enableBtns();
		}
		public function enableBtns():void {
			this.gotoAndStop("out");
			this.buttonMode = true;
			this.addEventListener(MouseEvent.ROLL_OVER, over);
			this.addEventListener(MouseEvent.ROLL_OUT, out);
			this.addEventListener(MouseEvent.CLICK, onClick);
		}
		public function disableBtns():void {
			this.gotoAndStop("over");
			this.removeEventListener(MouseEvent.ROLL_OVER, over);
			this.removeEventListener(MouseEvent.ROLL_OUT, out);
			this.removeEventListener(MouseEvent.CLICK, onClick);
		}
		private function over(event:MouseEvent):void {
			this.gotoAndStop("over");
		}
		private function out(event:MouseEvent):void {
			this.gotoAndStop("out");
		}
		private function onClick(event:MouseEvent):void {
			whichBtn = getChildIndex(DisplayObject(event.target));
			siteNav.btnClicked = whichBtn;
			siteNav.whichWay();
			trace(whichBtn);
			trace(event.target.name);
		}
	}
}

I’m not getting any error messages… but the “getChildIndex(DisplayObject(event.target))” is not returning the correct values… it’s always returning 0. When I use this method on the main timeline it works… but when I want to do it from inside a class I get 0’s. Also… when I trace the instance name of each button it returns values like “instance 20” despite the fact that I’ve manually given the movieclips instance names.

I’m obviously not understanding something about how display objects work in AS3. Any help would be appreciated.