如何在类别页面模板（wordpress）中列出类别的子类别

I have a categories page template, listing all categories with featured images. But I want to show only subcategories of a parent category. I don't know where to modify the template. Here is the code.

get_header(); ?>

<?php if(have_posts()) : ?><?php while(have_posts()) : the_post(); ?>

    <h1 class="border-radius-5"><?php the_title(); ?></h1>

        <div id="page" class="post-content">

            <?php the_content(); ?>

            <?php
                $terms = get_terms("category", $args);
                $count = count($terms);
                $categories = array();

                if ($count > 0) {

                echo '<ul class="listing-cat">';

                foreach ($terms as $term) {

                $args = array(
                    'post_type'        => 'post',
                    'posts_per_page'   => 1,
                    'show_count'       => 1,
                    'orderby'          => 'rand',
                    'post_status'      => 'publish',
                    'tax_query' => array(
                                        array(
                                            'taxonomy' => 'category',
                                            'field' => 'slug',
                                            'terms' => $term->slug
                                        )
                                    )
                );

                $video_from_categorie = new WP_Query( $args );

                if( $video_from_categorie->have_posts() ){

                    $video_from_categorie->the_post();

                }else{}

                $term->slug;
                $term->name;

            ?>

        <li class="border-radius-5 box-shadow">
            <?php echo get_post_image();?>

            <a href="<?php echo get_category_link( get_cat_ID($term->name) ); ?>" title="<?php echo $term->name; ?>"><span><?php echo $term->name; ?></span></a> 

            <span class="nb_cat border-radius-5"><?php echo $term->count; ?> <?php if ( $term->count > 1 ){
                _e( 'videos', get_theme_name() );
            }else{
                _e( 'video', get_theme_name() );
            } ?></span>                   
        </li>

    <?php
        }
        echo '</ul>';
        echo '<div class="clear"></div>';
        }
    ?>

    </div><!-- #page --> 

<?php endwhile; ?>

<?php endif; ?>

Pass the ID of the desired parent term/category to the child_of parameter of get_terms():

$terms = get_terms( 'category', array( 'child_of' => TERM_ID_GOES_HERE ) );