A chapter in Chemerinsky's casebook on Constitutional law is titled "Speech in Authoritarian Environments: Military, Prisons, and Schools."

Involuntary confinenent?

schools imprison kids now? really?

Kids can't just leave schools in the middle of the day, so basically yes.

You can’t leave your job in the middle of the day, so basically you’re a felon too?

This kind of meme nonsense belongs to reddit, not here

You can leave your job. You may not be allowed to return to it, but you can walk away.

You can switch your job as desired. Kids can’t switch their school.

You can not have a job (economic consequences aside). You can’t not be in school.

They didn’t choose to be there and if they hate it, the main way out is waiting.

Kids can’t switch their own school because they’re not their own legal guardians until they’re 18. You can’t switch nationalities just because you want to. That doesn’t make your country a penal colony.

You can OBVIOUSLY it be in school. No country on earth forces kids to join any school (let alone to attend it).

Most people didn’t choose to be at their jobs and hate it, the main way out is waiting for retirement.

Maybe this varies by location but at least in the UK, adults can usually leave the grounds of their place of work during a lunch break. Not true for school kids. And the difference in population density between schools and offices is usually stark.