You can do that with routing as you do in app which has normal django models from urls.py like this.
#urls.py
urlpatterns = patterns('',
url(r'^downloads/(?P<parent_id>\d+)/$', ParentView.as_view(), name='parents_list'),
url(r'^downloads/(?P<parent_id>\d+)/(?P<child_id>\d+)/$', ChildView.as_view(),
name='childs_list'),
)
Write corresponding views, and you should be fine. Please bear in mind, I have used Class Based Views in above url example. Just write whatever type of views you are familiar with.
The first view will show parent or parents list from given parent id in url. The second view will show child inside parent given parent and child ids.
Edit
Looks like your requirement is a bit complex, I found better solution here Django-MPTT full path to child pages how to make?
I hope it will solve your problem :)