WordPress: Automatically Apply Parent Page Template to Child Pages by Matovu Richard

wp-assign-parent-template.php

<?php
function switch_page_template() {
    global $post;
    // Checks if current post type is a page, rather than a post
	if (is_page())
	{	
		// Checks if page is parent, if yes, return
		if ($post->post_parent == 0)
			return true;
		else if ($post->post_parent != $post->ID)
		{
			$parent_page_template = get_post_meta($post->post_parent,'_wp_page_template',true);
 
			$template = TEMPLATEPATH . "/{$parent_page_template}";
			if (file_exists($template)) {
				load_template($template);
				exit;
			}
		}
	}
}
 
add_action('template_redirect','switch_page_template');

/* Source: http://www.matrich.net/blog/wordpress/how-to-automatically-apply-parent-page-template-to-all-sub-pages-in-wordpress.htm */
?>

Source: http://www.matrich.net/blog/wordpress/how-to-automatically-apply-parent-page-template-to-all-sub-pages-in-wordpress.htm