Show children connected to parent pages

Add this to you theme, just after the title part that displays the title.

<?php
$args   = array(
    'post_type' => 'page', // Only get pages (attachments can be listed as children)
    'posts_per_page' => -1, // List all the children
    'post_parent' => $post->ID // Get pages that are the children of the current page
);
$parent = new WP_Query($args);
if ($parent->have_posts()): // If there are any children
?>
<ul>
<?php while ($parent->have_posts()): $parent->the_post(); ?>
    <li><a href="https://wordpress.stackexchange.com/questions/365619/<?php the_permalink(); ?>"><?php the_title(); ?></a></li>
<?php endwhile; ?>
</ul>
<?php endif; wp_reset_postdata(); ?>