Wordpress - Display grandchild pages of current page

<?php
                                $postid = $post->ID;
                                $args = array(
                                'post_type' => 'page',
                                'post_status' => 'publish',
                                'orderby' => 'date',
                                'order'=> 'DESC',
                                'posts_per_page' => -1,
                                'post_parent' => $postid,
                                );
                                $child_level = get_posts($args);
                                if($child_level) :
                                foreach($child_level as $child_page) :

                                $args = array(
                                'post_type' => 'page',
                                'post_status' => 'publish',
                                'orderby' => 'date',
                                'order'=> 'DESC',
                                'posts_per_page' => -1,
                                'post_parent' => $child_page->ID
                                );
                                $my_query = null;
                                $my_query = new WP_Query($args);
                                if( $my_query->have_posts() ) {

                                while ($my_query->have_posts()) : $my_query->the_post(); ?>

                                <div class="product-box">
                                    <div class="product-content">
                                        <h1><a href="<?php the_permalink(); ?>"><?php the_title(); ?></a></h1>
                                        <div class="productimg"><?php the_post_thumbnail('thumbnail'); ?></div>
                                        <p><?php echo excerpt(15); ?></p>
                                        <p class="p-more"><a href="#product-<?php the_id(); ?>">More</a></p>

                                        <div class="product-details">
                                            <div class="pd-col">
                                                <p class="price">P<?php echo $cfs->get('prod_price', $pageChild->ID); ?></p>
                                                <!--<p class="rating"><img src="<?php bloginfo('stylesheet_directory'); ?>/images/rate0.png"></p>-->
                                                <p class="rating"><?php if(function_exists('the_ratings')) { the_ratings(); } ?></p>
                                            </div>
                                            <div class="pd-col">
                                                <a href="<?php the_permalink(); ?>"><div class="buyicon"></div></a>
                                            </div>
                                        </div><!-- product-details -->
                                    </div>
                                </div><!-- product-box -->

                                <?php endwhile;
                                }
                                wp_reset_query();

                                endforeach;
                                endif;
                                ?>
                        </div>