Sometimes when you divide up your WordPress content into categories it all ends up in sub-categories of one or two main categories that don’t have any content themselves. With the widget you can add a list of sub-categories even if the parent doesn’t have posts.
You can download this Widget from the WordPress Plugin Directory.
There is the option to use the title of the parent category as the widget title or you can enter a different title. Whichever title you choose there is an option to make that a link to the parent category.
You can choose to hide empty sub-categories (those without any posts) and you can also choose to show the number of posts in each sub-category.
If you want you can add a bunch of widgets, each showing sub-categories from a different parent.