Display a child page and its children only.

Hi,

I am working on a theme and I am stuck on the menu. The website has several child pages and those pages have children. What I want to achieve is when you click on a child page, it displays a menu with the child page and its children only.

Home
About
Events
-Event 1
-Event 2
–Venue
–Food
–Music
-Event 3
Contact

What I want is when I click on Event 2, It displays Event 2 and its children only.

My current solution displays all the child pages i.e. Event 1, Event 3. Please find my code below.

<?php
// find parent of current page
if ($post->post_parent) {
    $ancestors = get_post_ancestors($post->ID);
    $parent = $ancestors[count($ancestors) - 1];
} else {
    $parent = $post->ID;
}

$children = wp_list_pages("title_li=&depth=2&child_of=" . $parent . "&echo=0");

if ($children) { ?>

    <ul class="list-children">
        <?php echo $children; ?>
    </ul>

<?php } ?>