Nested Loop with custom Field

So what i want to be able to do is create a post that pulls multiple children posts into it using tagging or taximony and nested loops. Using the WordPress Codex I have found the basic setup that works:

<ul>
                    <?php if (have_posts()) : ?>
                        <?php while (have_posts()) : the_post(); ?>
                            <li>
                                   <?php $my_query = new WP_Query( "tag=CUSTOM_TAG" );
                                   if ( $my_query->have_posts() ) {
                                       while ( $my_query->have_posts() ) {
                                           $my_query->the_post();
                                           the_content();
                                       }
                                   }
                                   wp_reset_postdata(); ?>
                            </li>
                        <?php endwhile; ?>
                    <?php endif; ?>
                </ul>

The only problem is that TAG is static. When I create a new Parent post, i would like to create my own custom tag/taximony per post and asign that tag/taximony to any other child post i would like included under the parent post. Anyone have any ideas?