A shortcode to display the child pages of a parent page.

show-child-pages-on-parent.php

<?php
/**
 * A shortcode to display the child pages of a parent page.
 *
 * Usage: Simply embed [show_childpages_on_parent] on the parent page.
 * 
 */
add_shortcode('show_childpages_on_parent', function(){
	global $post;
	$html = '';


	$child_pages = get_pages( array( 
		'child_of' => $post->ID, 
		'sort_column' => 'post_date', 
		'sort_order' => 'desc' 
	));  	

	foreach( $child_pages as $page ) { 
		$id = $page->ID;		
		$content = $page->post_content;
		$title = $page->post_title; 		
		$excerpt = $page->post_excerpt;
		$permalink = get_permalink( $id );
		$thumbnail = '';


		if ( has_post_thumbnail( $id ) ){
			$thumbnail = '<div>' . get_the_post_thumbnail( $id, 'thumbnail', array( 'class' => 'alignleft' ) ) . '</div>';
		}

		if ( !$excerpt ){
			$excerpt = '<div>' . $thumbnail . wp_trim_words( $page->post_content ) . '</div>';
		} 

		$html .= '<div class="entry child-page-on-parent" style="clear:both"><h2><a href="' . $permalink . '">'. $title . '</a></h2>' . $excerpt . '</div>';	 
	}	 

	return $html;
});