Directory / plugin
Add Descendants As Submenu Items
v1.2.2 · by Alex Mills
Automatically all of a nav menu item's descendants as submenu items. Designed for pages but will work with any hierarchical post type or taxonomy …
About this plugin
When adding a page, category, or any hierarchical custom post type or taxonomy to your navigation menu (Appearance → Menus), this plugin allows you to optionally automatically add all descendants (children) of that menu item as submenu items.
In short, you’ll no longer have to manually maintain submenus when you add a new child page to your site.