I think what I want to do is quite the same as in the thread you linked to, but I need a 100% dynamical solution. My dad can’t edit templates and put in extra PHP-code every time he creates a new subpage.
I tried to edit the _page_level_out-function in WP, but it didn’t work perfectly. Subpages are now displayed if the parent is viewed, but not if one of the subpages is viewed. I replaced line 398 (i think) in template-functions-post.php with this:
if(isset($cur_page[‘children’]) && $_GET[‘pagename’] == $cur_page[‘name’]) {
