In your query posts array add this:
'meta_key' => (meta key name in database), 'meta_value' => 1
To make it at the top use two queries. One for the top first post and one for the rest of the posts/pages.
so your whole query will look like this:
<?php query_posts(array('showposts' => 1, 'post_parent' => $post->ID, 'post_type' => 'page', 'orderby' => 'title', 'order' => 'ASC', 'meta_key' => featured, 'meta_value' => 1); ?>
<?php if ( have_posts() ) : while ( have_posts() ) : the_post(); ?>
...
<?php endwhile; else: ?>
...
<?php endif; ?>
<?php wp_reset_query(); ?>
<second query goes here as you have it in your post>
Replace “featured” with your key name.