Add images from a specific post

Hi there,

I want to add images from a specific post. I#m using the following code.

function myGalleryShortcode() {
	$attachments = get_children( array('post_parent' => null, 'post_status' => 'inherit', 'post_type' => 'attachment', 'post_mime_type' => 'image', 'order' => $order, 'orderby' => 'rand', 'numberposts' => 6) );

	if ( empty($attachments)) return '';

	$output = "<div id='bildergalerie' class='gallery'><h2>Bildergallerie</h2>";

	foreach ($attachments as $id => $attachment ) {
			   $output .= '<a href="' .get_attachment_link($id). '">' .wp_get_attachment_image($id, 'thumbnail', false) . '</a>';
			   }

			   $output .= "</div>";

			   return $output;
	}

It shows me some pictures, but not from one specific page.
I think I have to change it in something like:
‘post_parent’ => singleID(123)

But how do I have to write it correctly to get the images from post number 123? Or am I completely wrong?

Thanks for your help.