Yeah no, that's not what I meant. Just let people be aware of the potential and make sure the kids are kept safe, for their own and society's good
You are not taking into account the potential negative repercussions here. If parents knew that their kid could be a psycho from an early age. And let that slip to the child. It could drive them to become psycho's in their early teens because teenagers like to do whatever will frighten their parents. In many ways, this preventative measure would cause more harm than good.
Even if the parents didn't let it slip, they might now over or under parent their children, due to the knowledge. Thus having potentially bad effects again.
I don't see a nett positive outcome from this suggestion in any way.
The breathalyzer analogy is a far different situation though. It is not a preventative measure designed to keep track of any potential offenders. It is simply a diagnosis tool, to determine if you are drunk at that time, if the cop has due cause to believe that you are.