Why are there no child categories in the open-cart 2 category module?

Question

opencart

Good afternoon.
For the first time I work with open-cart, I just pass the course.
In the header in the menu, I displayed a list of categories from the $categories array, and there I also displayed subcategories from $category['children'].
Now in the sidebar in $column_left I added a category module.
In the category.tpl file from the theme folder -> template -> extenstion -> module, I go through the $categories array, but the $category['children'] element has an empty array.
Maybe somewhere else you need to add a setting so that child categories are also displayed?
Code from category.tpl

<div class="col-xs-6 col-md-12">
    <div class="widget">
        <h3><?php echo $heading_title; ?></h3>
        <ul>
            <?php foreach($categories as $category): ?>
                <li>
                    <a href="<?php echo $category['href']; ?>"><?php echo $category['name']; ?></a>
                    <?php if($category['children']): ?>
                        <ul class="subcat">
                        <?php foreach($category['children'] as $child): ?>
                                <li> - <a href="<?php echo $child['href']; ?>"><?php echo $child['name']; ?></a></li>
                        <?php endforeach; ?>
                        </ul>
                    <?php endif; ?>
                </li>
            <?php endforeach; ?>
        </ul>
    </div><!-- .widget -->
</div>

And the result

Thank you in advance for your help.