Generate subcategories posts list

the following code let you display a list for every post under every subcategory of a selected parent category.

 <ul>
 <?php		
  $categories=  get_categories('child_of=6');  /// Parent Category number
  //echo  count($categories) . "<br/>";
  foreach ($categories as $cat) {
 	$var = $cat->cat_ID ;
	$lastposts = get_posts('category='.$var);
	echo "<h1>".$cat->cat_name. "  (" .count($lastposts)." posts )</h1>";
	echo "<ul>";
		foreach($lastposts as $post){
    		setup_postdata($post);
			echo "<li>";
			the_title();
			echo "</li>";
    	}
 	echo "</ul>";
  }
  
?>
 </ul>