Hmmm
Our module uses the bog standard VM product listing call
$productModel = VmModel::getModel('Product');
$products = $productModel->getProductListing($Product_group, $totalproducts, $show_price, true, false,$filter_category, $category_id);
this is in administrator/components/com_virtuemart/models/product.php line 1109
it has (surprisingly) no filtering of child products - you can see that in the code..
it passes it on to the function sortSearchListQuery function line 118 - again - no filtering of child products
so I guess this is what they intend...
I guess it either needs hacking there (cos this just returns a list of ids in a category) or add parents to a 2nd cat and target that with the slider or give the children full names..
Cheers