This plugin is very simple and straightforward. Just enter ?{list}? on each parent page or post where you want the children listed. Put it anywhere in your content and that is where it will show.
Then in your css..
.subpage-style { Put your styles here };
Easy as pie!

Andy's List Subpages Plugin

Nice and simple plugin that lists the children of a certain page or post in…

Alex Mills

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.

Add Descendants As Submenu Items

Still works great. Much better than Gecka Submenu - it doesn't break the layout on the menu screen and there's no unnecessary pro version upsell.  I hope this is updated at some point because its age is hiding it from WP's search results.



Works great and it's clean

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 …

Andy's List Subpages Plugin vs Add Descendants As Submenu Items