Displaying Child Page’s Information

Something like this would work:

<!--Child Page Thumbnails Start-->
<?php 
  $subs = new WP_Query( 
    array( 
      'post_parent' => $post->ID, 
      'post_type' => 'page', 
      'meta_key' => '_thumbnail_id' 
    )
  );
if( $subs->have_posts() ) : 
  while( $subs->have_posts() ) : 
    $subs->the_post();
    echo '<a href="'.get_permalink().'" title="'.get_the_title().'">'.get_the_post_thumbnail().'</a>'.'<br/><h2><a href="'.get_permalink().'">'.get_the_title().'</a></h2>';
  the_content();    
  endwhile; 
endif; 
wp_reset_postdata(); ?>
<!--Child Page Thumbnails End-->