New nodes using variable Follow

I have an abstract concept and few subconcepts that extend it. I created a node factory that creates one instance of each subconcept when new root node is created. Everything works when I specify subconcepts directly:

But when I want to create instances using a cycle through all subconcepts, add new() method is not accepting any parameter or expression. I expected the code to look like this, but this is not valid:

Thanks.
Tomas