'Quantity' and 'buy-button' disappeared

Hello,
I’m setting up a webshop for a client (first time).
Now he sell’s clothing and had to manually add a sizes box to every product trough ‘variable product‘. When publiced the sizes box shows neatly on the page, but the box where you can fill in a quantity and hit the buy button are disappeared.

Page without sizes box
Page with sizes box

Is there some way to get the quantity and button back under the sizes box?

Thanks in advance!

Rick

http://wordpress.org/extend/plugins/woocommerce/