Display child-page links in sidebar on both Parent Pages AND Child Pages

The following fixed the issue for me:

<?php
switch ($isBlogsPostPage){
    case true:
        $parentID=get_correct_id($post, $isBlogsPostPage);
        break;
    default:
        $parentID=get_correct_id($post);
}


$args = array(
    'post_type'      => 'page',
    'posts_per_page' => 10,
    'post_parent'    => $parentID,
    'orderby'        => 'menu_order'
 );
$parent = new WP_Query( $args );
if ( true ) : ?>

    <section class="links border shadow">
        <ul>
            <?php while ( $parent->have_posts() ) : $parent->the_post();?>

                    <li class="child-title <?php if ((is_page(get_the_ID())) || (get_the_ID()===(int) get_option( 'page_for_posts' ) && $isBlogsPostPage)) echo ('active'); ?>">
                        <a  href="https://wordpress.stackexchange.com/questions/336595/<?php the_permalink(); ?>" title="<?php the_title(); ?>"><?php the_title(); ?></a>
                    </li>
                    <?php /*endif;*/ wp_reset_postdata(); ?>    
            <?php endwhile; ?>
        </ul>
    </section>
<?php endif; wp_reset_postdata(); ?>