Display current category and child

$current_cat_id = get_queried_object_id();
$kids = get_terms([
    'taxonomy' => get_queried_object()->taxonomy,
    'parent'   => $current_cat_id,
]);

<?php

$terms = get_terms([
    'taxonomy' => get_queried_object()->taxonomy,
    'parent'   => get_queried_object_id(),
]);

echo '<div style="height: 200px; text-transform: uppercase; border:1px solid #666666; padding:10px; overflow-y: scroll;">
<ul>
foreach ( $terms as $term) {
    echo '<li><a href="' . get_term_link( $term ) . '">' . $term->name . '</a></li>';  
}
echo '</ul>
<br />';