Get Custom Post Child Term

Try this may be help you.

$terms = get_the_terms($post->ID, 'section' );

echo '<ul>'; 
      foreach ($terms as $term) {
           $term_slugs_arr[0] = $term->name;
           $termchildren = get_term_children( $term->term_id, 'section' );
           foreach ( $termchildren as $child ) {
                  $term = get_term_by( 'id', $child, $taxonomy_name );
                  echo '<li><a href="' . get_term_link( $child, $taxonomy_name ) . '">' . $term->name . '</a></li>';
    }
}
echo '</ul>';

OR

Check this Link