Using category templates on category children

Hi, I’m wondering if there is a way to have one template be used for a category and all it’s children. For example, I have one category called Portfolio (which is category 8) which has 4 children categories. I have a template file called category-8.php I want to work on all 5 categories (Portfolio + all it’s children). Right now it’s only working when I sort by Portfolio, but when I sort it by one of it’s children it’s loading up the index.php template. Is there any workaround without making 4 more template files?

Thanks,
David