Show all first level sub-categories on its parent's page

My question is so simple but, i cant found any solution. Basically i want to show first level sub-cat under parent page i’m using category images plugin here is the code `<?php

$args = array(
‘parent’ => 0,
);

foreach (get_categories($args) as $cat):

if (function_exists(‘z_taxonomy_image_url’) && z_taxonomy_image_url($cat->term_id) != null ): ?>
<div class=”col-md-3 col-xs-3 cat-index”>
<a href=”<?php echo get_category_link( $cat->term_id); ?>”
title=”<?php echo $cat->name; ?>”>
<figure class=”cat-img”>
<img class=”img-thumbnail” src=”<?php echo z_taxonomy_image_url($cat->term_id); ?>” alt=””>
<figcaption><?php echo $cat->name; ?></figcaption>
</figure>
</a>
</div>

<?php endif; endforeach; ?>`