Remove preinstalled apps on Big Sur MacBook Pro M1
The fastest path forward would be to make your account the administrator and grant each child their own managed AppleID and their own sign in and force them to abide by Screen Time limits.
You are correct that uninstalling the core parts of the system is a bit like the task of sysiphus.

https://support.apple.com/en-us/HT210387 (Guide on app restrictions)
https://support.apple.com/en-us/HT201084 (Guide on Family accounts)

You likely won’t even need to resort to stricter measures like a free / hosted MDM like https://app.jamfnow.com/devices
I have not had success messing with the Sealed System Volume (SSV) in Big Sur, but people are starting to document how this works publicly.