Expand children menu items with parent link, without javascript I've build a main-menu, and a sub-menu with Menu block. The sub-menu shows up if I'm on the article with the represented link. It works like it should.

Question: How can can I expand all childrens of a parent menu-link without Javascript?

A short wireframe for the overview.
If I understand you correctly then setting the parent link to "Show as expanded" should get you the desired result. You can see the option when you go to Structure -> Menus -> list links (of the correct menu) -> edit (the parent menu item which should have it's child links always displayed).