Notify butten when parent has no stock level ?

[TBoele]

I have a parent product with 2 childs.
I add a stockable custom field to my parent product, size M and L. Of each child product i have 1 in stock. The stock level of my parent is 0
When i go to my shop i see the parent product and i can select the size, but it shows the Notify button.

Do i also have set the stock level in the parent product, so both in the child and parent product ?