Display the title and thumbnail of child custom post types on the parent custom post type

gistfile1.txt

<?php
$pageChildren = get_pages('child_of='.$post->ID."&echo=0&post_type=custompostypename");
if ( $pageChildren ) {
  foreach ( $pageChildren as $pageChild ) {
	echo '<a href="' . get_permalink($pageChild->ID) . '">';
	$childimage = wp_get_attachment_image_src(get_post_thumbnail_id($pageChild->ID), 'thumbnail_size');
	$childimagealttext = get_post_meta(get_post_thumbnail_id($pageChild->ID), '_wp_attachment_image_alt', true);
	echo '<img src="'. $childimage['0'] . '" alt="' . $childimagealttext . '"/></a>';
	echo '<p><a href="' . get_permalink($pageChild->ID) . '">'. $pageChild->post_title.'</a></p>';
  }
}