System Software updates can cause difficulties for some users when new features are automatically enabled by the update, and/or some settings are reset. Your frustration is clearly understood.
You can certainly disable/remove the iPad Passcode if you wish - this having the side effect of completely disabling all security functions including TouchID/FaceID (as appropriate for the iPad model that you have). If Apps that you Son requires have no requirement for Passcodes, Passwords or other authentication, this might be a viable.
If contemplating this path, be mindful that you may encounter unanticipated consequences - however, should they occur, you can reinstate the iPad Passcode and restore full functionality if you need to do so. Also be aware that the iPad will have no protection whatsoever from unauthorised access.
Assuming that the iPad is not centrally managed by a third-party service provider, you can disable the iPad Passcode from settings:
Settings > TouchID | FaceID & Passcode > Turn Passcode Off
You would be wise to keep a written record of the device Passcode someplace safe. Doing so provides assurance that if, at some future time the Passcode is required, you have easy access to it.