Child theme throws errors when I try to use custom header.php

I created a child theme and needed to make a change to the header.php of the parent. So I copied the header.php to the child theme directory, and without even making any edits to it, it throws the following errors:

Warning: include(var.php) [function.include]: failed to open stream: No such file or directory in .../wp-content/themes/promotion-child/header.php on line 39

Warning: include(var.php) [function.include]: failed to open stream: No such file or directory in .../wp-content/themes/promotion-child/header.php on line 39

Warning: include() [function.include]: Failed opening 'var.php' for inclusion (include_path='.../wp-content/plugins/google-analyticator/google-api-php-client/src:.:/usr/lib/php:/usr/local/lib/php') in .../wp-content/themes/promotion-child/header.php on line 39

The header.php works fine when in the parent theme.

Any suggestions on what is causing the problem?

Thanks!

EDIT: Posting it here clued me in – I also had to copy var.php to the child theme.