对您的需求有一些想法。检查以下代码。。。

$parent=get_queried_object()->term_id;
$child = get_categories(\'child_of=\'.$parent. \'&hide_empty=0&echo=0&taxonomy=custom_taxonomy\');
    if(count($child)>0){
    $i=0;
     foreach ( $child as $row ) { $i++;
        echo \'<li><a href="\'.get_term_link($row,$row->taxonomy).\'">\'.$row->name.\'</a></li>\';
        if(count($child)==$i){
            $args=array( \'post_type\' => \'custom_post\',\'order\' => \'DESC\', \'posts_per_page\'=>1,\'tax_query\'  => array( array(\'taxonomy\' => \'custom_taxonomy\',\'terms\' =>$row->term_id, \'field\' => \'id\' )) );
            $second_query = new WP_Query( $args );
                if ($second_query->have_posts()) :
                    while ($second_query->have_posts()) : $second_query->the_post();
                        echo get_the_title();
                    endwhile; 
                endif; wp_reset_query();
        }
    }
}