Sign out is not available due to restrictions

I cannot "Sign Out" an AppleID on an iPhone 7 (iOS 13.6). I recently created an AppleID for a child (under 13) to be used on my iPhone 10. I signed into my iPhone with the child's AppleID and now I cannot sign out. "Sign out is not available due to restrictions" and "Sign Out" is not selectable. How do I Sign out a child's AppleID from this iPhone so I can use my own AppleID again?