如何在列出Wordpress菜单的子项时检索自定义链接？

I'm setting up a submenu to sit on the right hand side of my website. Currently I have it set up with wp_list_pages which lists all of the children pages.

However it's not showing any custom links I add in the main navigation. Can anyone point me in the direction of how best to get the custom links to show?

Here's my current code:

<!--sub menu side bar -->
<?php 
$PageArray = get_pages(array(
    'child_of' => get_the_ID()
));

if ($theParent or $PageArray) { ?>
<div class="page-links">
  <h2 class="page-links__title"><a href="<?php echo get_permalink($theParent); ?>"><?php echo get_the_title($theParent); ?></a></h2>
  <div class="wave_page-links"></div>
  <ul class="min-list">
    <?php
        if ($theParent) {
            $findChildrenOf = $theParent;
        } else {
            $findChildrenOf = get_the_ID();
        }
        wp_list_pages(array(
            'title_li' => NULL,
            'child_of' => $findChildrenOf,
            'sort_column' => 'menu_order', /*change page order in page attributes*/
        ));
    ?>
  </ul>
</div>
<?php } ?>