Adding the headings of direct children of the page to the page automatically. Just add the code below to the end of the content-page.php file in your theme directory.
<?php
$mypages = get_pages( array( 'parent' => $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
}
?>