Codeko

With this plugin you can set any post type (or posts types) as parent of any post type.
Urls will be wellformed, redirects will work, breadcrumbs will work fine.
This plugin is recomended when you need a url structure with a mix of post types. Any url structure you can imagine could be done.
Post types rewrite slugs will be ignored

Custom Posts Parents

Set any post type (or types) as parent of any post type. Any post structure can be created with this plugin.

WenZe

Category Parent Children Selector is a WordPress plugin that helps you in selecting parent-children categories.
Features include:
<ul>
<li>Button to select all categories. </li>
<li>Button to select all categories including children categories. </li>
<li>Button to select first level of children categories only. </li>
<li>Button to select parent and all its children categories under its sub categetory. </li>
<li>Auto select parent categories when a sub category is selected.</li>
</ul>

Category Parent Children Selector

Helps you in selecting parent-children categories.

Custom Posts Parents vs Category Parent Children Selector