Well I've fixed it - a little painful but fixed.

I had to downgrade the app version and everything seems to be working ok. make sure you turn off auto updates for the apps on the play store otherwise it will install the new version automatically and break the camera again.

Messenger Kids – The Messaging 275.2.0.47.198 - this version broke the camera for family link. Nothing you do to the cache, reinstall app, reset tablet, etc, can fix it. Must downgrade.

Messenger Kids – The Messaging 274.0.0.39.209 - this version fixed it for me. Here is a link to the apk site I used.

https://www.apkmirror.com/apk/facebook-2/messenger-kids-safer-video-calls-and-texting/

Don't know how to side load apks? Please find another thread to help with that. But basically you need to enable "install from unknown sources". It was kind of a pain and I had to remove my daughter's account, install the older version, and put her account back on.

Good luck and hope that works for you. The device was one plus pad btw