Populating Page with Child and Grandchildren

I don’t know the best way to describe my problem the topic title is true but it’s a little more complex than that. I’ve actually been able to populate using:

<?php
	$mypages = get_pages( array( 'child_of' => $post->ID, 'sort_column' => 'post_date', 'sort_order' => 'desc' ) );

	foreach( $mypages as $page ) {
		$content = $page->post_content;
		if ( ! $content ) // Check for empty page
			continue;

		$content = apply_filters( 'the_content', $content );
	?>
		<h2><a href="<?php echo get_page_link( $page->ID ); ?>"><?php echo $page->post_title; ?></a></h2>
		<div class="entry"><?php echo $content; ?></div>
	<?php
	}
?>

The problem I’m running into is that this isn’t what I was looking for. I really need to list the Child Page Title and immediately below that, list the first 5 Grandchildren (first one with the_thumbnail) of that Child Page with their own look.

With the code I have above, it just treats everything exactly the same. I’ve even designed a little mockup if my terminology is not up to snuff.

Am I going about this the right way? I’ve seen this done with posts/categories but they lack the power of templates that pages have.