Style sidebar menu list different for child and parent pages

Hi, I found a lot of answers on this forum, so I thank you all for your hard work and help.

My question today is, I am styling a menu for a friend and can’t figure out how to style the child pages different from the parent pages in his sidebar menu.

Here is the sidebar menu code:

<?php
$output = wp_list_pages('echo=0&depth=1&title_li=' );
if (is_page( )) {
  $page = get_query_var('page_id');
  if ($post->post_parent) {
    $page = $post->post_parent;
  }
  $children=wp_list_pages( 'echo=0&child_of=' . $page . '&title_li=' );
  if ($children) {
    $output = wp_list_pages ('echo=0&child_of=' . $page . '&title_li=');
  }
}
echo $output;
?>

Right now, it is all governed by a single div, but since the list is automatically generated, I don’t know how to style the children different.

Thank you all in advance, look forward to getting this fixed.