Dynamically link to child page WordPress

I'm using subpages on a WP site as follows;

Products (Parent Page) -Office (Subpage 1) --Office Gallery (Child of Subpage 1) -School (Subpage 2) --School Gallery (Child of Subpage 2) ....etc

How can I create a link on each subpage to its child page using just one template in my theme? I need to be able to give this link 开发者_如何学Pythona css class name. In other words I need to have the code in my page template look something like:

<a class="gallery-button" href="RETURN LINK TO CHILD PAGE OF CURRENT PAGE"></a>

or something like that......

I tried using wp_list_pages for a child page from the WordPress Codex but this returns a list and I really need just the permalink to the child page.

Is this easy? Impossible?

Thanks in advance.

You'll need to query posts to get the first child of the post in question;

<?php
    if ($children = get_children('post_type=page&numberposts=1')) {
        $first_child = $children[0];
        $first_child_permalink = get_permalink($first_child->ID);
        echo '<a class="gallery-button" href="' . $first_child_permalink . '">Link Text</a>';
    }
?>

Here's a revision of TheDeadMac's code I ended with that works in WP 3.9:

$children = get_pages("child_of=".$post->ID."&sort_column=menu_order");
$first_child = $children[0];
$first_child_permalink = get_permalink($first_child->ID);
echo '<a href="' . $first_child_permalink . '">Link Text</a>';