WordPress: List subpages on a parent page through a shortcode

gistfile1.txt

function wpb_list_child_pages() { 

global $post; 

if ( is_page() && $post->post_parent )

	$childpages = wp_list_pages( 'sort_column=menu_order&title_li=&child_of=' . $post->post_parent . '&echo=0' );
else
	$childpages = wp_list_pages( 'sort_column=menu_order&title_li=&child_of=' . $post->ID . '&echo=0' );

if ( $childpages ) {

	$string = '<ul>' . $childpages . '</ul>';
}

return $string;

}

add_shortcode('page_show_childpages', 'wpb_list_child_pages');

//# Instructions
// Put this in functions.php
// use shortcode [page_show_childpages] on page to list subpages
// if you need it automatically on every page, puts next code in the page template php file:
// <?php wpb_list_child_pages(); ?>


// source: http://www.wpbeginner.com/wp-tutorials/how-to-display-a-list-of-child-pages-for-a-parent-page-in-wordpress/

And if i want to order the pages by date?
What should i change?
Thanks!