这可以通过ne walker类完成

class Childcat2LastPost extends Walker_Category
{
    function start_el( &$output, $category, $depth = 0, $args = array(), $id = 0 ) {

        if ( 0 != $category->category_parent ) {

            $args = array(
                    \'cat\'            => $category->term_id,
                    \'orderby\'        => \'post_date\',
                    \'order\'          => \'DESC\',
                    \'post_type\'      => \'post\',
                    \'post_status\'    => \'publish\',
                    \'post__not_in\'   => get_option( \'sticky_posts\' ), // do not display sticky posts
            );

            $query        = new WP_Query( $args );
            $recent_posts = $query->get_posts();
            $last         = sizeof( $recent_posts ) -1;
            $last_post    = $recent_posts[$last];
            $permlink     = get_permalink( $last_post->ID );
            $title        = $last_post->post_title;

            if ( ! empty( $permlink ) ) {
                $output .= sprintf( \'<li><a href="%s">%s</a></li>\', esc_attr( $permlink ), esc_html( $title ) );
            }

        } else {

            parent::start_el( $output, $category, $depth, $args, $id );

        }

    }
}

必须将类作为参数传递给wp_list_categories

$cat2post = new Childcat2LastPost();

$args = array(
    \'walker\' => $cat2post
);

echo \'<ol>\';
wp_list_categories( $args );
echo \'</ol>\';

注释掉该行\'post__not_in\' 如果您想包含粘性帖子。调整HTML，使其与$output .= sprintf( \'<li><a href="%s">%s</a></li>\', esc_attr( $permlink ), esc_html( $title ) ); （添加alt 和/或title 属性、类等）。