Product listing page layout

My client wants to list subcategories on his product listing pages with product thumbnails displayed below each subcategory.
I have created the subcategories and have attached products to them.
But each product listing page now shows the main category with its subcategories below and no products. Only if I click a subcategory will I see the products.
How can I show everything on one page?
I don't want to have to click a subcategory to see its products.

There is no option for that. If you want to do it, you will have to edit the files of the view product via the menu Display->Views but it means that you need to know PHP...

Thanks for the quick response!