Loop that displays PARENT PAGE & CHILD PAGE & outputs GRANDCHILD PAGE title and content

I’ve never posted here, but I’m tired of slapping code together. That said, I would be most appreciative if someone could help me with this.

I need a page template that:

1. outputs the PARENT PAGEs,
2. the CHILDREN PAGES of that PARENT PAGE,
3. and finally output the titles and content of the GRANDCHILDREN PAGES so I can insert them into a tabbed layout.

Here’s a diagram:

The idea is that visitors should be able to get to the content on the GRANDCHILDREN PAGES in two clicks.

For the PARENT PAGES, I’m using wp_nav_menu.

For the CHILD PAGES, I’m using:

    <?php if ( is_page() ) { ?>
    <?php
    if($post->post_parent)
    $children = wp_list_pages('title_li=&child_of=".$post->post_parent."&echo=0'); else
    $children = wp_list_pages('title_li=&child_of=".$post->ID."&echo=0');
    if ($children) { ?>

    <ul class="child-pages">
    <?php echo $children; ?>
    </ul>
    <?php } } ?>

And to output the GRANDCHILDREN PAGES title and content, I’m using some code from the codex:

GRANDCHILDREN PAGES

<ul class="nav nav-tabs" id="myTab">
<?php
$pages = get_pages('child_of=".$post->ID."&sort_column=post_date&sort_order=desc');
$count = 0;
foreach($pages as $page)
{
    $content = $page->post_content;
    if(!$content)
        continue;
    if($count >= 100)
        break;
    $count++;
    $content = apply_filters('the_content', $content);
?>

<li>
<a data-toggle="tab" href="#<?php echo $count ?>"><?php echo $page->post_title ?></a>
</li>

<?php } ?>
</ul>

GRANDCHILDREN CONTENT

<div class="tab-content">

<?php
    $pages = get_pages('child_of=".$post->ID."&sort_column=post_date&sort_order=desc');
    $count = 0;
    foreach($pages as $page)
    {
        $content = $page->post_content;
        if(!$content)
            continue;
        if($count >= 100)
            break;
        $count++;
        $content = apply_filters('the_content', $content);
    ?>


<div class="tab-pane" id="<?php echo $count ?>">
<?php echo $content ?>
</div>

<?php } ?>
</div>

I am certain there is a more efficient way to do without a gazillion loops and queries.
Anyone have any ideas? I’m want to learn, and put code an elegant solution.