Why do I get a "too many Apple IDs created on this device" error when I have not created any Apple IDs yet?

Brand new iMac. Trying to create three child accounts for Family Sharing so I can use Screen Time parental controls for the kids' user accounts. Every time I try to create a child's Apple ID, I either get a "cannot connect to iCloud" error or a "too many Apple IDs created on this device" error. It will not let me create any Apple IDs. I have never successfully created an Apple ID on this device. And from all I can tell, I am connected to iCloud. What is going on and how can I fix it?