Display sub-categories on category page

I'm attempting to have my sub-categories displayed on a category page, just as I did on the main shop page, but I haven't been able to find anything about this. Shouldn't sub-categories show up by default?

Main shop page: http://drrubinstein.server304.com/shop

Category page: http://drrubinstein.server304.com/shop/products/category/jan-marini-skin-research/

Sample sub-category: http://drrubinstein.server304.com/shop/products/category/jan-marini-skin-research-c-esta-line/

Thank you!