[Django]-Django child url does not show its template

That’s because you don’t have the end of string match ($) at the end of the regular expression:

url(r'^campaigns/$', views.campaigns, name='agency-campaigns'),
#            HERE^

Or, you can also put the “agency-add-campaign” pattern before the “agency-campaigns”:

url(r'^campaigns/add/$', views.add_campaign, name='agency-add-campaign'),
url(r'^campaigns/', views.campaigns, name='agency-campaigns')