Just do this :
package code {
import flash.display.MovieClip;
import flash.events.MouseEvent;
public class Main extends MovieClip {
public var redBox: Box = new Box();
public function Main() {
// constructor code
stage.addEventListener(MouseEvent.CLICK, mouseClickEvent);
}
public function mouseClickEvent(e:MouseEvent):void {
redBox.x = stage.mouseX;
redBox.y = stage.mouseY;
addChild(redBox);
}
}
}