Peter Westwood

This plugin allows you to run loops within your WordPress templates where you query for children of the current page.
The plugin extra arguments to the list of arguments supported by query_posts().
The query argument <code>child_of</code> is used to add a WHERE to the database query to limit the pages returned to those with a post_page equal to the argument provided.
The query argument <code>child_limit</code> is used to limit the number of pages returned.
The query argument <code>child_offset</code> is used to offset the limiting to allow for pagination if required.

PJW Query Child Of

This plugin allows you to run loops within your WordPress templates where you query for children of the current page.

hildende

With installing this plugin you add functionality to <code>wp_nav_menu()</code> to show 
only children of the current page or start with a specific navigation level.

Child Navigation

Adds support for child navigation to wp_nav_menu()

PJW Query Child Of vs Child Navigation