Screen time keeps turning off on my child's phone

I have 2 children tagged to my apple account. I enabled screen time on both their devices. For one child, screen time is working just fine. For the other, screen time just keeps disabling itself totally.

Symptoms: I enable screen time on my child's device. I set downtime. App limits. A passcode. All the settings. I see them set on the child's phone. 30 seconds later.... my phone says screen time is not enabled on my child's device. And checking his device, screentime isn't there at all.

Troubleshooting done:

1. I've logged out of iCloud and back in on my child's device. No fix.
2. I've logged out of iCloud and back in on my own device. No fix.
3. I've restarted both devices along with the log-in/log-out. No fix.

I've seen this problem on other discussions, but there's no resolution. Does any one have any magic fix please? Screentime is invaluable to managing my kids device time.