<?php

global $post;

$exclude = [];
foreach(get_pages(['meta_key' => '_wp_page_template', 'meta_value' => 'guidance-note-template.php']) as $page) {
    $exclude[] = $page->post_id;
}

$children = get_pages( array( 'child_of' => $post->ID ) );
$hasChild = (count( $children ) > 0 );
$page_id = ($hasChild) ? $post->ID : wp_get_post_parent_id( $post->ID );
    wp_list_pages( array(
    'title_li'    => '',
    'child_of'    => $page_id,
    'exclude'      => implode(",", $exclude),
));
?>