get_pages_wp_list_pages.php

<?php
 	$children = wp_list_pages(array(
 			'title_li'     => '',
 			'child_of'     => $post_id,
 			'sort_column'  => 'menu_order',
 			'post_status'  => 'publish',
 			'echo'         => 0
	 ) );

	$children = get_pages( array(
		'child_of'     => $post_id,
		'sort_column'  => 'menu_order',
		'hierarchical' => 0,
		'depth'        => 0
	) );