您的代码有太多错误，启动WP\\U查询时没有\'sort_column\' , 或\'depth\' 参数。使用$do_not_duplicate = $post->ID; 什么都不做，还有其他一些事情。

您需要的是获取子项（仅ID，无需获取post对象，因为您不使用除标题和premlink之外的任何字段），对它们进行循环，并为每个子项获取子项（意味着主页孙子）并对其进行循环。

类似这样：

<?php   
//store page
$temp = $post;
//get children
$children = get_posts(array(
    \'orderby\'  => \'menu_order\',
    \'post_per_page\' => 30, 
    \'post_parent\' => $post->ID, 
    \'post_type\' => \'page\',
    \'fields\' => \'ids\')
);
//children loop
foreach ($children as $child) {
    $do_not_duplicate[] = $child;
    ?>
    <div id="child">
        <h2 class="clear"><a href="<?php echo get_permalink($child); ?>" ><?php echo get_the_title($child); ?></a></h2>
    </div> <?php
    //get grandchildren
    $grandchildren = get_posts(array(
        \'orderby\'  => \'menu_order\',
        \'post_per_page\' => 3, 
        \'post_parent\' => $child, 
        \'post_type\' => \'page\',
        \'fields\' => \'ids\')
    );
    $count = 0;
    //grandchildren loop
    foreach($grandchildren as $granchild){
        setup_postdata($granchild);
        $count++;
        if ($count == 0){ ?>
            <div id="top">
                <div class="first">&nbsp;</div>
                <h3 class="clear"><a href="<?php the_permalink($granchild); ?>" ><?php the_title($granchild); ?></a></h3>
                <?php echo get_the_post_thumbnail($granchild->ID, \'thumbnail\'); ?>
                <p class="clear"><?php the_content(\'read more...\'); ?></p>
            </div> <?php 
        }elseif ($count == 1){ ?>  
            <div class="middle">
                <h3><a href="<?php the_permalink(); ?>" ><?php the_title(); ?></a></h3>
                <p class="clear"><?php the_content(\'read more...\'); ?></p>
            </div> <?php
        }else { ?>  
            <div class="last">
                <h3><a href="<?php the_permalink(); ?>" ><?php the_title(); ?></a></h3>
                <p class="clear"><?php the_content(\'read more...\'); ?></p>
            </div><?php
        }
    }
}
//restore page
$post = $temp;

像这样的方法应该会奏效：

$args = array(
    \'sort_column\' => \'menu_order, post_title\',
    \'child_of\'    => $post->ID,
    \'parent\'      => $post->ID,
    \'hierarchial\' => 0,
);
$children = get_pages( $args );

foreach( $children as $child ) {
    $child_args = array(
        \'sort_column\' => \'menu_order, post_title\',
        \'child_of\'    => $child->ID,
        \'parent\'      => $child->ID,
        \'hierarchial\' => 0,
        \'number\'      => 3
    );

    $grandchildren = get_pages( $child_args );

    setup_postdata( $child );
    ?>
    <h1><?php the_title(); ?></h1>
    <?php
    $first = true;
    foreach( $grandchildren as $gchild ) {
        setup_postdata( $gchild ); ?>
        <?php if( $first === true ) : ?>
            <div class="first">
                <!-- do your output -->
        <?php else : ?>
            <div class="middle">
                <!-- do your output -->
        <?php endif; ?>
            </div>
        <?php
        if( $first === true )
            $first = false;
    }
}