Oh, yeah, I definitely can't see the parents being arrested, even if their kid went through with a terrorist attack. We don't even arrest the parents of school shooters. In some rare cases of juvenile radicalization, maybe the prosecutor would refer the case to CPS, but only if they thought the parents were somehow responsible for causing the problem in the first place. But if there is an actual problem then they'd throw the kid in jail, so there would be no need for CPS.