Animating Instances of an Object Created by a For Loop

I'v been toying with this for a few weeks now and I'm trying to find the best way to animate several instances of an object created by a for loop thru an ENTER_FRAME function. When the function runs only 1 of the 3 instances that were created animates.

var balloonArray:Array = new Array();
var balloon: hotAirBalloon;
var xVel: Number = -3;
var yVel: Number = -4;

addEventListener(Event.ENTER_FRAME, startBalloons)

for(var i:int=0; i<3; i++)
         {
             balloon = new hotAirBalloon;
             addChild(balloon);
             //balloonArray.push(balloon) // tried pushing the instances in an array
             setBalloons();
         }

function setBalloons():void
     {
         balloon.x = randomRange(200, 400);
         balloon.y = randomRange(400, 550)
         balloon.scaleX=balloon.scaleY=randomRange(0.3, 1);
     }

function startBalloons(evt:Event):void
    {
        balloon.y += yVel// this only animates one instance

        balloon.x += xVel
     }

I also tried pushing the object into an array in the for loop and using this balloonArray.y += yVel in the ENTER_FRAME function and I get an error saying that a term is undefined. I know there is a simple way to achieve this. Thanks.