>actually preparing a terrorist attack right?

For that we already have a law, planing for a crime.

But that law really just means you have sympathy or contact to potentially dangerous persons, or you speak out stuff that could be connected to "terrorism".

They even invented a new Word for that (in Germany): Gefährder (a potential dangerous person who did not broke any law...)

EDIT: Actually it look's like 12yo don't have to go to prison but have to stay at home.