Random headerimage for mother and childpages

Hi,

I would like to have a different headerimage for certain pages and all the childpages. The code below shows how you can set a particular image for a specific page, but I would also like to do this for all childpages.

div id="header_img">
        <?php if (is_page('archives')) { ?>
        <img src="<?php bloginfo('template_url'); ?>/images/header_archives.jpg" width="790" height="140" alt="<?php bloginfo('name'); ?> archives page header image" />
        <?php } elseif (is_page('about')) { ?>
        <img src="<?php bloginfo('template_url'); ?>/images/header_about.jpg" width="790" height="140" alt="<?php bloginfo('name'); ?> about page header image" />
        <?php } else { ?>
        <img src="<?php bloginfo('template_url'); ?>/images/header_<?php echo(rand(1,5)); ?>.jpg" width="790" height="140" alt="<?php bloginfo('name'); ?> random header image" />
        <?php } ?>
    </div>

Can some tell my how an image can be used for the childpages aswell? Many thanks, Sugar