page.php

<?php
  get_header();
  while( have_posts() ) {
    the_post();
    pageBanner();
?>

    <div class="container container--narrow page-section">
<?php 
    // theParent is true if current page is a child page
    $theParent = wp_get_post_parent_id( get_the_ID() );

    if ( $theParent ) { ?> 
      <div class="metabox metabox--position-up metabox--with-home-link">
        <p><a class="metabox__blog-home-link" href="<?php echo get_permalink( $theParent ) ?>"><i class="fa fa-home" aria-hidden="true"></i> Back to <?php echo get_the_title( $theParent ); ?></a> <span class="metabox__main"><?php the_title(); ?></span></p>
      </div>   
    <?php    
    }
    ?>

    <?php 
    $hasSubPages = get_pages( array(
      'child_of' => get_the_ID() //lists the sub pages of the current page (children/grandchilds)
    ));
    
    /* don't show links for single pages */
    if ($theParent or $hasSubPages) { ?>
      <div class="page-links">
        <h2 class="page-links__title"><a href="<?php echo get_permalink( $theParent ); ?>"><?php echo get_the_title( $theParent ); ?></a></h2>
        <ul class="min-list">
          <?php 
            if ( $theParent ) {
              $findChildrenOf = $theParent;
            } else {
              $findChildrenOf = get_the_ID();
            }
            
            wp_list_pages( array(
              'title_li' => NULL, /* no heading and list items will not be wrapped */
              'child_of' => $findChildrenOf
            ));
          ?>
        </ul>
      </div>
  <?php
  }
  ?>
      
      <div class="generic-content">
        <?php the_content(); ?>
      </div>

    </div>

<?php 
  }
  get_footer();
?>