Add this code to your functions.php. An explanation of the code is given below.
function wpb_list_child_pages() {
global $post;
$id = ( is_page() && $post->post_parent ) ? $post->post_parent : $post->ID;
$childpages = wp_list_pages( 'sort_column=menu_order&title_li=&child_of=" . $id . "&echo=0' );
//you can add `&depth=1` in the end, so it only shows one level
if ( $childpages ) {
$string = '<ul>' . $childpages . '</ul>';
}
return $string;
}
add_shortcode('wpb_childpages', 'wpb_list_child_pages');
Explanation
The code checks to see if a page has a parent or the page itself is a parent. If it is a parent page, then it displays the child pages associated with it. If it is a child page, then it displays all other child pages of its parent page. Lastly, if this is just a page with no child or parent page, then the code will simply do nothing. So just add this shortcode [wpb_childpages] to the page where it’s child pages will be displayed.
My test output that worked at my localhost:
Test1
-t1
–tt1
-t2
and the output that displays when I wrote that shortcode in Test1 page is:
t1
t2