ActionScript 3.0 :: How Does SetChildIndex(); Work?

For the life of me, I cannot understand this method. The help files are confusing to me, and I can't locate anything else on the web that explains how it works.

What I have is an array of 5 objects closely in a row, that tween and expand on a MOUSE_OVER. Trouble is, I want the object to be in front of the others on the MOUSE_OVER, but part of it is always beneath the object to its right or left. Here's the code I have:


Code:
import fl.transitions.*;
import fl.transitions.easing.*;

addEventListener(Event.ENTER_FRAME, setupVars);

function setupVars(e:Event):void {
trace("Entering setupVars");
//The following removes the Event.ENTER_FRAME listener so that it does not activate 30 times a second.
removeEventListener(Event.ENTER_FRAME,setupVars);
var myArray:Array = [box1_mc, box2_mc, box3_mc, box4_mc, box5_mc];
for(var i:Number = 0; i < myArray.length; i++) {
myArray[i].addEventListener(MouseEvent.MOUSE_OVER, boxOver);
myArray[i].addEventListener(MouseEvent.MOUSE_OUT, boxOut);
myArray[i].buttonMode = true;
}
}
var box:Tween;
var box2: Tween;
function boxOver(ev:Event):void {
box = new Tween(ev.target, "width", Elastic.easeIn, 100, 130, .5, true);
box = new Tween(ev.target, "height", Elastic.easeIn, 100, 130, .5, true);
trace("yay, it works")
}

function boxOut(ev:Event):void {
box2 = new Tween(ev.target, "width", Elastic.easeOut, 130, 100, 1, true);
box2 = new Tween(ev.target, "height", Elastic.easeOut, 130, 100, 1, true);
trace("yay, this one works, too")
}
Could someone be so kind as to help me with the setChildIndex method? I want any particular box to be in front of the others on the OVER.