Display ALL the child category of a specific parent category in single product

Hi, i’ve look for display by list, the sub-category of 3 catégory parent.
I find this code in this forum which works well…only one point : it’s display only one of the sub-category and not ALL the sub-category,
anyone have a idea ?

<?php
global $post;
$sou_cat = get_term_by('slug', 'PARENT-CAT-SLUG', 'product_cat');

$terms = get_the_terms($post->ID, 'product_cat');
foreach ($terms as $term) {
    if($term->parent === $sou_cat->term_id) { ?>
       <span class="product-sub-cats"><?php echo $term->name; ?></span>
      <?php  break;
    }
}
 ?>

thanks a lot !