Not understanding createChildSymbol

I have a square symbol on the stage: squareHolder

In the Library I have a symbol called: circle

In document.compositionReady I have this code

     sym.mySymbol = sym.createChildSymbol('myCircle', 'squareHolder');

I have a button on the stage with the following code:

     sym.$('myButton').click(function(){

        sym.$('squareHolder').children().remove();

       })

When I click on the button, I expect the circle to disappear but the squareHolder symbol also disappears.

I am not understanding where the new childSymbol called mySymbol lives. I thought it was inside the squareHolder symbol so I could access it by using

sym.getSymbol('squareHolder').getSymbol('mySymbol')

but that isn't working