Display posts belonging to child term

I was able to get this working with the following code. I used the relation operator AND, referenced the var ($this_term) that contained get_queried_object(); to set the taxonomy in the tax_query and adjusted the term field in the tax_query.

 $this_term = get_queried_object();
 $args = array(
'parent' => $this_term->term_id,
'orderby' => 'slug',
'hide_empty' => false
 );
 $child_terms = get_terms( $this_term->taxonomy, $args );
 echo '<ul>';
 foreach ($child_terms as $term) {

 // List the child topic
 echo '<li><h3><a href="' . get_term_link( $term->name, $this_term->taxonomy ) . '">' . $term->name . '</a></h3>'; 

 // Get posts from that child topic  
$query = new WP_Query( array(
  'post_type' => 'kb',
  'tax_query' => array(
    'relation' => 'AND',
    array(
      'taxonomy' => $this_term->taxonomy,
      'field'    => 'slug',
      'terms'    => array( $term->slug )
    )
  )
) );

 // List the posts
 if($query->have_posts()) {
      while($query->have_posts()) : $query->the_post(); ?>
           <li><a href="<?php the_permalink(); ?>" title="<?php the_title_attribute(); ?>"><?php the_title(); ?></a></li><?php
      endwhile;
 } else  { echo "no posts";}


 // close our <li>
 echo '</li>';
 } //end foreach

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