Merkuri
Explorer
I know I'm a bit late to the party, but what about setting the admin account to have a password and not letting the kid have that password?
That would not prevent the kid from booting into safe mode. Choosing what mode to boot into happens before Windows is loaded (and thus, before you log in). However, it may be possible to restrict certain users from being able to log in while in safe mode. I'm not sure how to do this, but I wouldn't be surprised if it's possible.
So, you'd have two accounts on the machine, one is an administrator and one is a "normal" user that is not allowed into safe mode. If you guard the administrator password carefully and pick something the kid won't be able to guess then he or she could still cause the machine to boot into safe mode but wouldn't be able to do anything at that point because the one user account they have access to can't log into safe mode.