WordPress: Register a shortcode to list child pages on a parent page

wp_list_child_pages.php

<php

// Turn on excerpt support for pages by enabling them in your themes functions.php file

add_post_type_support( 'page', 'excerpt' );

/* Add the below function to your theme's functions.php file
** This has more capabilities than get_pages and wp_list_pages
** Usage: [list_subpages aclass="button" ifempty="Sorry, we currently don't have any job openings."]<h3>List of Jobs</h3>[/list_subpages]
*/

// List Subpages in a List
function dk_list_child_pages( $atts, $content = "" ) { 
 	global $post; 
 	
 	$atts = shortcode_atts( array(
 			'ifempty' => 'No Records',
 			'aclass' => ''
 	), $atts, 'list_subpages' );
 	
 	$args = array(
 	    'post_type'      => 'page',
 	    'posts_per_page' => -1,
 	    'post_parent'    => $post->ID,
 	    'orderby' => 'publish_date',
 	    'order' => 'DESC',
 	);
 	
 	$parent = new WP_Query( $args );
 	
 	if ( $parent->have_posts() ) {
 		$string .= $content.'<ul>';
 		while ( $parent->have_posts() ) : $parent->the_post();
 			$string .= '<li><a class="'.$atts['aclass'].'" href="'.get_permalink().'" title="'.get_the_title().'">'.get_the_title().'</a>';
 			if ( has_excerpt( $post->ID ) ) {
 			 	$string .= ' - '.get_the_excerpt();
 			}
 			$string .= '</li>';
 		endwhile;
	} else {
		$string = '<p>'.$atts['ifempty'].'</p>';
	}
	wp_reset_postdata();
	return $string;
 }
add_shortcode('list_subpages', 'dk_list_child_pages');