How displaying text in child?

Question

-I got two movie clips in library (s1 and s2).
-Got text filed in each movie clips ($text1 and $text2)
I wrote the code to show the texts of two movie clips.
However, s1 showed the text, s2 doesn't. Why?
Attachment for reference.http://hotfile.com/dl/126771818/ed3ea02/test-addchild-display_text-cs4.fla.html
import flash.display.MovieClip;
var a:MovieClip =new s1();
a.x=stage.stageWidth/2;
a.y=stage.stageHeight/2;
addChild(a);
var b1:MovieClip = new s2();
b1.x=stage.stageWidth/2-150;
b1.y=stage.stageHeight/2-150;
a.addChild(b1);
a.$text1.text="a";
a.b1.$text2.text="b";

Answer 1

Just to demo the first approach I mentioned using getChild...()-type methods...
var a:MovieClip =new s1();
a.x=stage.stageWidth/2;
a.y=stage.stageHeight/2;
addChild(a);
var b1:MovieClip = new s2();
b1.name = "b1_s2_mc";
b1.x=stage.stageWidth/2-150;
b1.y=stage.stageHeight/2-150;
a.addChild(b1);
a.$text1.text="a";
MovieClip(a.getChildByName("b1_s2_mc")).$text2.text="b";