Flex: View Stack Navigator

I have a component mxml file in which i have a view stack, on click of a button i navigate to the first child, now i need to navigate to the second child during onclick of a button present in the second child. All the childs are component files included within the view stack. How could this be done, Sample code is present below,

--------------------Application.mxml---------------------

<mx:Canvas xmlns:mx="http://www.adobe.com/2006/mxml" >
    <mx:Script>
        <![CDATA[
             private function loadScreen():void
             {
                navigationViewStack.selectedChild=id_offering;  
             }
        ]]>
    </mx:Script>

     <mx:Button label="Save" click="loadScreen();"/>

 </mx:Canvas>

<mx:ViewStack id="navigationViewStack"  width="100%" height="100%">
    <components:dashboard   id="id_dashboard" label="Dashboard" />
    <components:offering   id="id_offering" label="Offering" />
    <components:IssueSec id="id_issueSec" label = "Issues"/>
</mx:ViewStack>

-------------------------Ends--------------------------------------

Now in my offering.mxml file if i try to access navigationViewStack i am getting an error stating 'Access of undefined property navigationViewStack.

Help me on how to access the view stack from my component mxml file.

Thanks!

Cheers, Deena

Custom event is the correct and appropriate way to go; if you want a quick and dirty solution that will eventually become difficult to maintain as your code base grow, you can try this from the button click handler in the Offering.mxml:

ViewStack(this.parent).selectedIndex = 2; //2 for IssueSec