Children list

/* Function.php */
function wpb_list_child_pages() {

global $post;

if ( is_page() && $post->post_parent )

    $childpages = wp_list_pages( 'sort_column=menu_order&title_li=&child_of=' . $post->post_parent . '&echo=0' );
else
    $childpages = wp_list_pages( 'sort_column=menu_order&title_li=&child_of=' . $post->ID . '&echo=0' );

if ( $childpages ) {

    $string = '<ul class="wpb_page_list">' . $childpages . '</ul>';
}

return $string;

}

add_shortcode('wpb_childpages', 'wpb_list_child_pages');

/* Style */
ul.wpb_page_list {
    list-style: none;
    list-style-type: none;
    background-color: #eee;
    border: 1px solid #CCC;
    padding: 20px;
}

/* Shortcode */
[wpb_childpages]

<?php wpb_list_child_pages(); ?>