cart variant child product problem

[Commpro]

Hello,

I have a website with kids clothing.
I've set up childproducts for some of them and the first one that is loaded when you enter the product page does not go through as a variant.
When you click a different size in the pulldown the site reloads and it works fine.

This used to work before I updated to 2.6.6

Can someone help me out?
Link: http://www.springscollection.nl/index.php?option=com_virtuemart&view=productdetails&virtuemart_product_id=427&virtuemart_category_id=40&Itemid=249

So if you go to this page and you add to cart it adds the head product instead of the first child.
If you select a different size and add it it works.

I hope someone has the answer.
Thanks in advance!

Bert
CommPro