Calling & Displaying Attachments from Sub-Pages - Wordpress

Hi I'm new to wordpress (duh) and trying something I'm very close to getting.

I have several Sub-Pages, each of which have attachments - images. I simply want to display these images. The client will regularly be adding more subpages so the code has to know to only display the images of it's self, so to speak. An issue I'm running into is each subpage is displaying all the attachments of all subpages.

In my Functions.php I have this code to determine if the page is infact a subpage:

//find out if it is a suppage to use in page.php as function 'is_subpage'
function is_subpage() {
    global $post;                              // load details about this page

    if ( is_page() && $post->post_parent ) {   // test to see if the page has a parent
        return $post->post_parent;             // return the ID of the parent post

    } else {                                   // there is no parent so ...
        return false;                          // ... the answer to the question is false
    }
}

In my page.php I have an If statement, for all my usual pages. It culminates in this:

        elseif ( is_subpage() ) {
      get_template_part( 'exhibition-template' );
      get_template_part( 'normalfooter' );
    }

In exhibition-template.php, where I want my images to appear I have this:

    <?php

if ( is_subpage( $post->ID ) ) { //I think I screwed up here, innermost brackets


$args = array(
    'order'          => 'ASC',
    'post_type'      => 'attachment',
    'post_parent'    => $post->ID, //or is my issue here...?
    'post_mime_type' => 'image',
    'post_status'    => null,
    'numberposts'    => -1,
);
$attachments = get_posts($args);
    if ($attachments) {
        foreach ($attachments as $attachment) {
            echo wp_get_attachment_link($attachment->ID, 'large', false, false);
        }
    }
}

?>

However, what happens is each and every subpage simply displays all the images across all subpages, and frankly I'm just too DUMB to know how to progress, or what to play with, where to start. Any ideas? THANKS!