[WordPress] Display Post or Page Children in custom MetaBox

WP_display_children_metabox.php

<?php
// This requires that your post type is hierarchical obviously (like Pages)

// Display all children of this post/page in a custom metabox below title
function display_msg_for_parents( $post ) {
	$children = get_pages(array('child_of' => $post->ID, 'post_type' => get_post_type($post->ID),));
	if(!empty($children)) { ?>
		<div class="rp_children postbox">
			<button class="handlediv button-link" aria-expanded="true" type="button">
				<span class="screen-reader-text">Toggle panel: Children</span>
				<span class="toggle-indicator" aria-hidden="true"></span>
			</button>
			<h2 class="hndle ui-sortable-handle">
				<span>Children</span>
			</h2>
        	<div class="inside">
        		<p>This Post has the following children:</p>
        		<ul>
					<?php foreach($children as $child) {
						echo '<li><a href="'.get_edit_post_link($child->ID).'" target="_blank">'.$child->post_title.'</a></li>';
					} ?>
				</ul>
			</div>
    	</div>

	<?php }
	wp_reset_postdata();
}
add_action( 'edit_form_after_title', 'display_msg_for_parents' );

?>