WP as CMS – Check if child page is current

I am trying to put together a WP powered-CMS for a client.
It will be a bunch of pages, subpages, subsubpages and on.
I’ve figured out how to highlight where am I in subpages with a code found here.

The problem is the main menu. All works fine if I am on one of main pages…than I get “current” in LI class. When I select a subpage of main page the “current” class is gone from main menu.

Is there a code or something that will return in listpages “if child or subchild of this parent is selected” than put “class=”selected” in parent too?

Thanks in advance.
I’ve checked some plugins …they’re working fine but none of them solved my specific problem. Maybe there is someone of WP punters that resolved this before? I’ve found several simmilar threads….but none dealing with this problem.