Wordpress query one post from each parent category (exclude child categories)

I'm trying to list one post from each parent category in Wordpress but I can't seem to figure out how to alter this code to exclude child categories. Basically I'm listing the name of the category, then a post thumb, an excerpt, and a read more button for each parent category. I cannot just exclude child categories by category id because this site is for a client who will be adding sub categories later on. Please help, thanks!

$num_cats_to_show = 10;
$count = 0;
$taxonomy = 'category';//  e.g. post_tag, category
$param_type = 'category__in'; //  e.g. tag__in, category__in
$term_args=array(
  'orderby' => 'name',
  'order' => 'ASC',
);
$terms = get_terms($taxonomy, array( 'exclude' => '15,1'),$term_args );
if ($terms) {
  foreach( $terms as $term ) {
    $args=array(
      "$param_type" => array($term->term_id),
      'post_type' => 'post',
      'pos开发者_运维技巧t_status' => 'publish',
      'posts_per_page' => 1,
      'caller_get_posts'=> 1,
      );
    $my_query = null;
    $my_query = new WP_Query($args);
    if( $my_query->have_posts() ) {
      $count ++;
      if ($count <= $num_cats_to_show) {
        while ($my_query->have_posts()) : $my_query->the_post(); 

I think you want to get only those terms that have a parent equal to 0 (no parent).

$term_args = array(
  'orderby' => 'name',
  'order' => 'ASC',
  'parent' => 0
);
$terms = get_terms($taxonomy, $term_args);

I don't think you can exclude terms by ID with get_terms, but you can just reject the relevant terms in your loop.