Wordpress template redirection for child pages. Adopt Parent template if its assigned.

parent_template.php

// Custom Template Inheritance -----------------------------
  function custom_template_override () {
		if( is_page() ) {
			global $post;

			if( $post->post_parent ) {
				
				$parent_page_template = get_post_meta($post->post_parent,'_wp_page_template',true);
				$current_page_template = get_post_meta($post->ID, '_wp_page_template' , true );
				
				if ( $parent_page_template !="default"  && $current_page_template == "default" ) {
					include ( TEMPLATEPATH ."/". $parent_page_template );
					exit;
				}
				
			}
			
	/*		echo TEMPLATEPATH."<h1>$parent_page_template</h1>";
	*/
		}
	}

	add_action( 'template_redirect','custom_template_override' );