Adding Movieclips with addchild and a loop...how to target a specific one?

1

I have this code:

for(var i:Number = 0; i < 10; i++) {

    buttonVar = new button();
    addChild(buttonVar);  
    buttonVar.x = i*120;

}

It creates a 10 movieclips and moves them apart 120 units, what I want is to target a specific created movie clip. Say for example the number 4 in the loop, how can I asign a specific instance to that movieclip? to differentiatte it from the other ones ? any idea ?