Hello guys. I'm having this very same need as a couple years ago somebody shared in these forums: http://wordpress.org/support/topic/admin-select-all-categories?replies=3, and to no avail.
I have a site with a bunch of parent categories with about 7-20 child categories each, and I need a way to be able to automatically select all the childs when I select its parent. Moreover, a "Select All" categories link would be helpful too. I did a thorough search in the plugin repo and didnt find anything.
Is there any solution? any plugin? function? filter? someone?