Three types of prison

(1) "Correctional facilities" are prisons for convicted criminals,
(2) "Schools" are prisons for children, and,
(3) "Hospitals" are prisons for sick people.

The thing that makes each of these a prison is that the inhabitants are not allowed to leave in each case without permission.

Attendance at school is compulsory, you don't have a choice, if you play by the government rules. They will attempt to punish you if you do not.

Hospitals can be left when well but until then you are at their mercy!