addClass not working

Well, I’ve got a little Problem.
I want to add a class to my dropdownmenu (wp_list_pages) which is applied only to li elements with a submenu (ul with class children).
I tried to use the jQuery code below but it doesn’t apply the class. With a .css(…) it works fine but thats no very dynamic.

jQuery('ul.children').parents().addClass('has_children');

<nav class="page-nav">
<ul>
<li class="page_item">point 1
<ul class='children'>
<li class="page_item>subpoint 1</li>
</ul>
</li>
</ul>
</nav>