How to unlock non owner account after reboot? I've an Android 9 Samsung tablet. I've set up normal (I.e. not limited) accounts for my children.  When the tablet reboot, the only account which is usable is mine. The others are greyed out. When I've logged in once, the other accounts are unlocked.

I'd like my children to be able to use the tablet after a reboot without me needing to log in. How can I achieve that? 

I found this question which seems similar but it has no answers.
It seems like by definition the primary user (here called "user 0") has to log in by definition as the first user. The documentation on the File Based Encryption (FBE) does not give many details on the question why:


  Each user in a multi-user environment gets a separate encryption key. Every user gets two keys: a DE and a CE key. User 0 must log into the device first as it is a special user. This is pertinent for Device Administration uses.


Source: https://source.android.com/security/encryption/file-based#supporting-multiple-users

Hence I don't see a chance to change this behavior, you can only teach your children not to reboot the tablet and not to switch it off. In air plane mode with really disabled Wifi the battery loss should be minimal so that the tablet can stay on even when it is not used for some days.