How Can I Create Multiple Symbol Children With Code?

I want to create multiple instances of a movieclip (linkage name "my_circle") and control their positions with code. I want to name the instances circle1, circle2, circle3, etc. I tried using EVAL with the code below. It doesn't work.

var itemName = "circle";

var evalName;

for (var i = 1; i < 5; ++i) {

     evalName = eval("itemName + i");

     evalName  = new lib.my_circle(); // create instance

     evalName.x = Math.floor(Math.random() * 400); // position instance

}

this.addEventListener("tick", fl_AnimateHorizontally.bind(this));

function fl_AnimateHorizontally() {

  circle1.x+=10;

}