Eric: I just noticed it works when I choose the actor in the drop down in the details panel. Thats awesome! I am one step closer 
BUT I would like to set it up from an array. when I Plug the exact same actor in the target slot of the add child actor node it does not work anymore. My Goal would be like described above choose some actors and make an array from them ( that allready works) and plug them into the add child actor node, but for some reason this does not work.
HAH: yes Problem is I dont know how to add random child actors from array.