Wordpress List Child Pages with Thumbnails

wordpressListChildPages.html

<?php if (is_page('web-design')) : ?>
 <?php $i = 0; ?>
 <div>
 <ul>
 <?php  
 $args = array(
 'post_parent' => $post->ID,
 'post_type' => 'page',
 'post_status' => 'publish',
 'orderby' => 'menu_order',
 'order' => 'ASC',
 'numberposts' => -1,
 );
 $postslist = get_posts($args);
 foreach ($postslist as $post) :
 setup_postdata($post);
 $i++;
 ?>
 <li>
 <h3><a href="<?php the_permalink(); ?>"><?php the_title(); ?></a></h3>
 <div><a href="<?php the_permalink(); ?>"><?php if( has_post_thumbnail() ) the_post_thumbnail('thumbnail'); ?></a></div>
 <div>
 <?php the_excerpt(); ?> &mdash;<a href="<?php the_permalink(); ?>">Read more</a>
 </div>
 </li>

 <?php endforeach; ?>
 </ul>
 </div>
 <?php endif; ?>