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](https://android.stackexchange.com/questions/183542/how-can-i-allow-a-second-user-account-to-unlock-my-device-after-a-reboot) which seems similar but it has no answers.