List All Categories and Subcategories and return the last post register

functions.php

<?php
/**
* Returns ID of top-level parent category, or current category if you are viewing a top-level
*
* @param    string      $catid      Category ID to be checked
* @return   string      $catParent  ID of top-level parent category
*/
function smart_category_top_parent_id ($catid) {
    while ($catid) {
        $cat = get_category($catid); // get the object for the catid
        $catid = $cat->category_parent; // assign parent ID (if exists) to $catid
        // the while loop will continue whilst there is a $catid
        // when there is no longer a parent $catid will be NULL so we can assign our $catParent
        $catParent = $cat->cat_ID;
    }
    return $catParent;
}

nav.php

<ul id="menu-menu-principal" class="nav navbar-nav">
<?php

	$cats = get_terms( 'category', array(
			'hide_empty' => 0,
			'orderby'    => 'menu_order'
		)
	);

	foreach ($cats as $cat) {
		
		$cat_id = $cat->term_id;

		$args = array(
			'post_type' 	 => 'post',
			'orderby' 	 => 'menu_order',
      			'order' 	 => 'ASC',
			'cat' 		 => array( $cat_id ),
			'posts_per_page' => 1,
		);

		$loop_cat = new WP_Query( $args );

		if ($loop_cat->have_posts()) : while ($loop_cat->have_posts()) : $loop_cat->the_post();

			/* Verifica o ID da categoria Parent */
			$category = get_the_category($post->ID);
			$catid = $category[0]->cat_ID;
			$top_level_cat = smart_category_top_parent_id ($catid);

			/* Adiciona a class menu-parent se existir Parent Category */
			if($cat->parent == 0 ){
				$addClass = ' menu-item-has-children';
			}else{
				$addClass = ' menu-item-hiden menu-parent-' . $top_level_cat; 
			};
		?>				
			<li id="menu-item-<?php echo $cat->term_id; ?>" class="menu-item menu-item-type-taxonomy menu-item-object-category menu-item-<?php echo $cat->term_id . $addClass; ?>">
				<a href="<?php the_permalink();?>" title="<?php echo $cat->name; ?>"><?php echo $cat->name; ?></a>
			</li>
			<?php
		endwhile; endif;
	wp_reset_postdata(); 
	};
?>
</ul>