Wordpress: Add a subpages menu

wordpress-subpages-menu.php

<?php

function subpages() {
    global $post;
    
    // Output a link to the parent page, if we are on a subpage
    if (!empty($post->post_parent)) {
        $title = esc_attr(get_the_title($post->post_parent)) ?>
        <p><b>Parent page:</b><br />
        <a href="<?php echo get_permalink($post->post_parent); ?>" title="<?php echo esc_attr($title); ?>"><?php echo $title ?></a></p>
    <?php }

    // Output a menu of subpages only if current page has any subpages.
    $params = array('child_of' => get_the_ID(), 'title_li' => null);    
    // You may want to add a title here. Something like "Table of Contents" or
    // "Subpages".
    if (count(get_pages($params))) { ?>
    <ul class="entry-toc"><?php wp_list_pages($params) ?></ul>
    <?php }
}