Query posts of all subcategories

Hello everybody,

I’m a little bit confused. I would like to query all posts from subcategories from one specific category. I thought child_of would work, but it seems that it doesn’t with query_posts.

For example: I have the category ?Fruits?. Within this category I have the categories ?Apples? and ?Peaches?. So I would like to query all posts of the categories ?Apples? and ?Peaches?. But there are all the time new subcategories added, so I can’t name them directly. Just the parent category stays the same all the time.

Any ideas??
Thanks in advance!
Karina