I'm developing a theme for someone, and they need a lot of category navigation. The goal is for each parent category page to display a list of its children categories. However, if we're at the deepest categories where actual content begins, it should display posts instead of categories.
So essentially I want to tell WordPress'
archive.php page that
if is_category() and the category has children, display the kiddies. If it doesn't, display posts.
How do I tell WordPress to do that?