Right now, the gameobject set in the Actor Group, has to be the same with the one having the Animation component.
In other words, using the Animation from a child gameobject is not possible, so the only way now, would be to create another Actor Group that has that child gameobject as target actor.
In the next version though, using the Animation component from a child gameobject of the actor, will be possible since this is a highly requested feature 🙂