selecting child layer separately from parent

[jenwa8]

Hello! I'm new to editing in layers, so this may seem like a simple question.  For some reason, when I want to select a child layer (like a mask, for example) to edit, the parent layer is also automatically selected. I've tried to click and unlike the "edit all layers" icon, but nothing changes.  Is there a setting I'm missing here?  Thanks for your advice! 

 

Jenny

[R C-R]

Try clicking on the thumbnail of the mask layer.