Great, glad it is useful.
You should be able to exclude child products by modifying the SQL query in the galleryXML component. The file that you need to modify is the frontend file
components/com_vmgalleryxml/models/vmgalleryxml.php
the line that you need to modify is either
$q .= "product_publish='Y' ";
which you will want to modify to
$q .= "product_publish='Y' AND product_parent_id='0' ";
or
$q .= "AND #__vm_product.product_publish='Y' \n";
which you will modify to
$q .= "AND #__vm_product.product_publish='Y' AND #__vm_product.product_parent_id='0' \n";
Each of these lines occur several times, so you will need to make sure you find the correct one, or change it in all cases.
If you are used to php it is quite simple, but if you are not then I realise it could be a bit confusing. I would be happy to send you a modified file if you need it.