It’s one with fifty sovereign states with their own criminal justice and judicial systems. So the question really should be, You can jail children in Tennessee?
The majority of the US states have no minimum age of criminal responsibility. Other ex-colonial federations have states with their own laws and courts, too, yet do not have this problem.
In fact, the US is the only country in the world to lack these legal protections.
In fact, the US is the only country in the world to lack these legal protections.