Submenu classes

<?php
								if (is_page( )) {
                  $page = $post->ID;

                  if ($post->post_parent) {
                    $page = $post->post_parent;
                  }

                  $children=wp_list_pages( 'echo=0&amp;child_of=' . $page . '&amp;title_li=' );

                  if ($children) {
                    $output = wp_list_pages ('echo=0&amp;child_of=' . $page . '&amp;title_li=');
                  }

                }

              echo $output;

              ?>

Thats my current code, works fine. But i have a question, how can i add the class “first” at the first item, and “last” and the last items?