Actionscript 3 :: Flex 3: Determine If A Generic Object Is Actually A Button?

I have this bit of code, and it's not working as I expected. btnContainer is a VBox that contains a ton of buttons (toggle=true); and I want to reset them to un-toggled at a certain point.

for (var btn:Object in btnContainer.getChildren()){
if (btn.isPrototypeOf(mx.controls.Button)){
btn.selected = false;
}
}

With the above code, "btn" shows up as just the index during each iteration of the loop (0,1,2,3,...), and the conditional never evaluates to true.I also tried this:

for (var btn:Button in btnContainer.getChildren()){
btn.selected = false;
}

This works fine, except that there is also a label inside btnContainer; so it throws an error when trying to cast the label as a button.