tell a child gotoAndPlay(X) from a code in timeline of another child.

Hi there!

I have tried to simplify my bigger question in the following example.

(Also you may download this FLA if needed)

what do I have:
- an EMPTY scene.
- 2 movieclips in library (m1mc , m2mc)

I use addChild method to add them to stage (m1=m1mc , m2=m2mc). this is the code in Frame 1 of empty scene:

var m1:m1mc = new m1mc();
var m2:m2mc = new m2mc();

addChild(m1);
addChild(m2);

m1.x = 100;
m2.x = 300;

"m1mc" contains some frames that in frame 1 I have asked it to stop:

stop();

And finally my questions is:

HOW to write a code in frame 1 of "m2mc" (that is in library) to tell "m1mc" gotoAndStop frame 2 (in this example)??

I CAN access and change the alpha of "m1mc" from the timeline of "m2mc" with this code:

parent.getChildAt(0).alpha = 0.5; //works fine

but I CAN'T use the same method to tell "m1mc" gotoAndStop(someFrame)

parent.getChildAt(0).gotoAndStop(2);

//Error Symbol 'm2mc', Layer 'Layer 2', Frame 1, Line 2 1119: Access of possibly undefined property gotoAndStop through a reference with static type flash.display:DisplayObject.

Any help would be highly appreciated