Testing Collision Between Multiple Object Of The Same Class

Okay, so I have a function on the Main Timeline that creates an instance of the class Ball once every 60 frames (1 second). In the class code for Ball I have this:

package {
    import flash.display.MovieClip;
    import flash.events.*;

    public class Ball extends MovieClip {
        private var _root:Object;
        private var distY:Number;
        public function Ball() {
            addEventListener(Event.ADDED_TO_STAGE, beginClass);
        }
        private function beginClass(event:Event):void {
            _root=MovieClip(root);
            addEventListener(Event.ENTER_FRAME, eFrame);
        }
        private function eFrame(event:Event):void {
            this.y+=1;
            for (var i:int=0; i<_root.numBalls; i++) {
                var mc:Ball=Ball(getChildAt(i));
                for (var j:int=0; j <_root.numBalls; j++) {
                    var mc2:Ball=Ball(getChildAt(j));
                    distY=Math.abs(this.y-_root.getChildByName("Ball"+i).y);
                    if (distY<=this.height) {
                        trace("STOP");
                    }
                }
            }
        }
    }
}

As you can see, I am trying to make it so that if two instances of the class Ball collide, then it should output “STOP”. But it isn’t working. Can anyone please tell me what I am doing wrong?