<?php $counter = 1 ?>
<div class="row-fluid">
<?php
$pages = get_pages('child_of='.$post->ID.'&sort_order=asc&sort_column=menu_order&parent='.$post->ID);
foreach($pages as $page) { ?>
    <h2><?php echo $page->post_title ?></h2>
    <?php
    $the_query = new WP_Query( array(
            'post_parent' => $page->ID,
            'orderby' => 'menu_order',
            'order' => 'ASC',
            'posts_per_page' => 3,
    ));
    while ( $the_query->have_posts() ) :
    $the_query->the_post();
    ?>
        <div class="span4">
            <h2><a href="<?php the_permalink() ?>"><?php the_title() ?></a></h2>
            <?php the_content(); ?>
        </div>
    <? if ($counter % 3 == 0): ?>
    </div>
    <div class="row-fluid">
            <?php endif; ?>
    <?php $counter++; ?>
    <?php
        endwhile;
        wp_reset_postdata();
} ?>
</div>