WordPress > snippet > get child category id

childlist.php

<?php
if (is_category('example') || in_category('example')) {
    if (!is_front_page()) {
        $cat = get_category_by_slug('example');
        $cat_id = intval($cat->cat_ID);
        $url = get_category_link($cat_id);
        $name = $cat->name;
?>
        <h2><a href="<?php echo esc_url($url); ?>"><?php echo esc_html($name); ?></a></h2>
        <ul>
            <?php wp_list_categories('child_of=' . $cat_id . '&hide_empty=0&title_li=&show_count=0'); ?>
        </ul>
<?php
    }
}
?>