To hide the children page!

Hi,
i have a little problem with a theme!
I hope that this forum’s branch is the correct for my problem.

In my header i’ve this code’s part:

<li class="<?php if ( is_home() or is_archive() or is_single() or is_paged() or is_search() or (function_exists('is_tag') and is_tag()) ) { ?>current_page_item<?php } else { ?>page_item<?php } ?>">
<?php wp_list_pages('sort_column=menu_order&depth=1&title_li='); ?>

When the depth’s value is equal 1, i know that the children page would be invisible, but in my theme i see this pages.

Someone could me help with this problem?
Thanks a lot