This is a working code. If you place the code in proper place it will surely gonna work [inshALLAH]. You can use this as a function or even shortcode.
global $post;
$parent_id = $post->ID; //if you are within a loop
$childpages = new WP_Query([
'post_type' => 'page',
'post_parent' => intval( $parent_id ),
'posts_per_page'=> 3, // your choice
'orderby' => 'menu_order', // your choice
'post_status' => 'publish'
]);
if( $childpages->have_posts() ) :
echo '<ul>';
while( $childpages->have_posts() ) : $childpages->the_post();
echo '<li><a href="'. esc_url(get_the_permalink()) .'" rel="bookmark">'. esc_html(get_the_title()) .'</a></li>';
endwhile; wp_reset_postdata();
echo '</ul>';
endif;