Deleting images attached to a post

I would like to have all the images that are attached to a post or custom post type be deleted when my client deletes a post.

I understand that images may be attached to more than one post, but in my situation that is not the case at all.

I have seen and tried this solution:

function delete_post_children($post_id) {
	global $wpdb;
	$ids = $wpdb->get_col("SELECT ID FROM {$wpdb->posts} WHERE post_parent = $post_id AND post_type = 'attachment'");
	foreach ( $ids as $id )
		wp_delete_attachment($id);
}
add_action('delete_post', 'delete_post_children');

but it doesn’t seem to work.

Also, manually deleting unattached images just isn’t a viable option.

Any help would be greatly appreciated 🙂