post type and category not working together in query

What I am trying to do is be able to find a random attachment in the category.php page belonging to one of the posts in that category and also be able to find a random attachment in the single.php belonging to that post.

What I have been able to get so far is to find a random attachment in a single post.

$images =& get_children( array(
	'post_parent' => $post -> ID,
	'post_type' => 'attachment',
	'post_mime_type' => 'image',
	'orderby' => 'rand',
	'numberposts' => 1
) );
foreach ( (array) $images as $attachment_id => $attachment ) :
	echo wp_get_attachment_url( $attachment_id ) . '<br>';</script>';
endforeach;

I tried adding ‘cat’ => 1, but it doesn’t display anything.

I tried following the example http://codex.wordpress.org/Template_Tags/get_posts#Random_posts and output the titles to test it. I set post_type to attachment and it shows all the attachments in all categories. I set cat to 1 and it does not show anything (I know I have 1 attachment in 1 of the posts there). I delete post_type and it shows the post titles for cat 1.