Could grounding your child be considered false imprisonment?

Is there an exception because the child is in the custody of their parent?

So when did proper discipline of a child be considered a crime?

Minors do not have the same constitutional rights as adults. Provided you feed him and educate him and such, you can keep him in his room as long as you want!

Probably not, but depending on the potential you’ve raised him to before grounding, you could be charged with murder.