chilpages-looping.php

<?php 

/**
 * Notes and things that I changed:
 *  -- fixed indentation and spacing for WP standards
 * 	-- posts_per_page = -1 is dangerous, what happens if the site has 1000000 posts, the server will explode - find a high but sane limit
*/

// loop through the sub-pages of your custom post type
$childpages = new WP_Query( array(
	'post_type'      => 'work', 
	'post_parent'    => $this_page,
	'posts_per_page' => 100,
	'orderby'        => 'menu_order'
	) ); 
while ( $childpages->have_posts() ) : $childpages->the_post(); ?>

	<section>

		<h2 class="title"><a href="#"><?php the_title(); ?></a></h2>
		<div class="content">
			<?php the_content();?>

			<?php $this_subpage = $post->ID; ?>

			<?php 
			//Loop through the sub-pages of the child pages next
			$subpages = new WP_Query( array(
				'post_type' => 'work', 
				'post_parent' => $this_subpage,
				'posts_per_page' => 100,
				'orderby' => 'menu_order'

				));

				while ( $subpages->have_posts() ) : $subpages->the_post(); ?>
				<section class="subpages">

					<h3><a href="#"><?php the_title(); ?></a></h3>
					<div>
						<?php the_content();?>
					</div>
				</section>
			<?php endwhile; wp_reset_query(); ?>

		</div><!--.content -->
	</section>
<?php endwhile; wp_reset_query(); ?>

Good point about posts_per_page. Didn't think about that.
I think that gist is messing about with my indentation.