Sorry to say but as you know the Products and Categories are handled by WooCommerce. So, it is default working from WooCommerce end with the default WordPress Themes like Storefront too that the Child Category Products are also shown in Parent Category: https://snipboard.io/iBw8Nt.jpg
So, this structure is followed from WooCommerce end and you can contact the WooCommerce Support in this regard. They might help you with that.