Sollie - 3:34 pm on Sep 11, 2012 (gmt 0)

This seems to be working fine;

I added the code below to functions.php

"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
}
}"

And added the following to my widget;
"is_page(446) || is_subpage(446)"
446 being the page_id of the parent post.