Adding an IF Function to Current Custom Category If has Child

If you asking about $terms has child then only go for it. With this you can try below code as solution:

<?php (
    $terms = get_terms([
        'taxonomy' => get_queried_object()->taxonomy,
        'parent'   => get_queried_object_id(),
        'hide_empty' => false
    ]));
    // get_terms will return false if taxonomy does not exist or term wasn't found.
    // term has children
    if($terms){
        echo '<div style="height: 200px; text-transform: uppercase; border:1px solid #666666; padding:10px; overflow-y: scroll;">
                        <div class="breaker-small">Refine Search</div>';
                         foreach ( $terms as $term) {
                            echo '<p class="filters"><a href="' . get_term_link( $term ) . '">' . $term->name . '</a></p>';  
                         }
        echo '</div><br />';
    }
?>

I hope my this code work for you!