Remove Child from Diferent Timeline

programming flash
1

How do I remove child from a different Timeline. One of my movieclip contains three children. I want to remove all the three children. How could I do that. I tried setting instance name and removing the instances using getChildByName. But it doesn’t seem to work.

var mainMc:MovieClip = new MovieClip();
addChild(mainMc);
var box:box_mc;

var objLength:int;
for (var i:int = 0; i<3; i++) {
    box= new box_mc;
    mainMc.addChild(box);
    box.x=i*100;
    box.name="box"+i;
    objLength=i;

}

remove_mc.addEventListener(MouseEvent.CLICK, clickHandler);
function clickHandler(event:MouseEvent):void {
    for (var i:int=0; i<=objLength; i++) {
        mainMc.removeChild(getChildByName("box"+i));
    }
}