Slider loop

slider_loop.php

<?php 
 $page_ID = $post->ID;
 $lightbox_id = 1; // important to set lightbox id outside the loop

 $q = new WP_Query( array( 'post_type' => 'page', 'post_parent' => $page_ID, 'depth' => 1, 'posts_per_page' => -1 )  );
 if ( $q->have_posts() ) : while ( $q->have_posts() ) : $q->the_post();
   $slider_array = array(get_field('slider_1') , get_field('slider_2') , get_field('slider_3') ,  get_field('slider_4'));

?>

<?php foreach ($slider_array as $slide) :?>
  <div class="col-xs-6 col-pages">
      <a href="<?php echo $slide['sizes']['large'] ?>" data-lightbox="<?php echo 'localisation_'.$lightbox_id ?>">
          <div class="page-img-miniature" style="background: url('<?php echo $slide['sizes']['medium'] ; ?>') no-repeat center; background-size:cover"></div>
      </a>
  </div>
<?php endforeach;  $lightbox_id = $lightbox_id + 1?>