[Plugin: WP-PostViews] Include child categories ?

I have lots of child categories with parents categories left empty (i mean not checked when i publish a post). I would like to use “get_most_viewed_category” to display most viewed post for a category including child categories but this seems impossibile to reach.

Is there some trick to show parent and child categories most viewed post with “get_most_viewed_category function”? Alternatively, is there a way to pass multiple categories ids to “get_most_viewed_category” function?