NON CHAOS SPACE.
Say it with me. NON CHAOS SPACE.
EG, places without already summoned demons flitting about. The fabric of reality is too thick there for them to just pop in and say "hello!"
Re vaccination:
True belief-- Yes. You would teach them that they can manifest their own wills within the immaterium, and in the true world. The simulations would teach them to do that, before they actually gain the powers to do so. this is the "vaccination". Their own belief in their own wills, would give them the vaccine.
Kot, you keep returning and beating a dead horse with the "But its a simulation!" routine. How do you know that the christians AREN'T RIGHT? You really dont, do you? You only have the signals your body gives your mind from the world around you to go by, and you conclude, through lack of supporting sensation, that no such outside reality exists.
The fact that it is a simulation is meaningless. It's as faithful a simulation of real reality as can be given, but the kids are already indoctrinated that it is fake, VERY VERY VERY early in the process. Like nursery school level.
Instead, they are given lessons, using the fact that it is indeed a simulation, that as closely mimic the experience of being submersed into the immaterium provides, as possible-- with guided instruction, and positive feedback. They are trained to transform that experience, and rewarded for doing so.
When the change comes, they know exactly what to do-- Reshape the immaterium to protect themselves.