<?php
    $mypages = get_pages(
    array(
    'child_of' => $post->ID,
    'sort_column' => 'post_title',
    'sort_order' => 'ASC',
    'depth'        => 0,
 )
 );

foreach( $mypages as $page ) {

    ?>

<div class="hoerspiel-genre-grid">
    <div class="left">
        <div class="hoerspiel-genre-grid-bilder">
        <a href="<?php echo get_page_link( $page->ID ); ?>">
              <?php echo get_the_post_thumbnail( $page->ID, 'medium' ); ?>
        </a>
        </div>
    </div>
  <div class="right">
      <div class="hoerspiel-genre-grid-titel">
      <a href="<?php echo get_page_link( $page->ID ); ?>">
            <?php echo $page->post_title; ?>
       </a>
      </div>

      <div class="hoerspiel-genre-grid-text">
          <?php echo $page->post_excerpt; ?>
      </div>
  </div>
</div>

    <?php
    }
?>