James Irving-Swift

Electric Studio

Adds a filter in your wp-admin that allows you to choose a parent page so that only the children of that page will be shown. Very useful if you have a lot of pages! 
Thank you to Brian Krogsgard for the changes in version 1.3 (Twitter: @Krogsgard)

Filter Pages by parent in admin

Filter pages in the wp-admin by their parent pages

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.

Filter Pages by parent in admin vs Category Parent Children Selector