Remove Admin Rights

No, unless something's amiss with the system, if m-d-c has an account with administrator rights, then as long as s/he's logged into that administrator account, s/he can remove the admin rights for any other account. I do that quite regularly, for various reasons. If it's not working for you, make sure you've unlocked the preference.

Regards.

Open Accounts preferences when logged into your admin account. Click on the lock icon and authenticate. Select the other account and uncheck the box labeled, "Allow user to administer this computer." Check the other box labeled, "Enable Parental Controls." Click on the Parental Controls button to configure.

I believe that option will be grayed out unless he's logged into his daughter's admin account. (I didn't know that but just tried it).

Then log into the New admin account and set parental controls for the daughter's account.

Hmm, wasn't grayed out for me while logged into my own account. But one way or the other should do the trick.

When you tried from your own account, was your daughter's account logged out? You can't change her account if it is still logged in via Fast User Switching.

Did you click on the lock icon and authenticate?

No. All admin accounts are the same. Sounds like if you've done what's been suggested, then your system may be corrupted in some way. If it is then you will need to reinstall Snow Leopard.

Reinstalling Snow Leopard

Boot from your Snow Leopard Installer disc. After the installer loads select your language and click on the Continue button. When the menu bar appears select Disk Utility from the Utilities menu. After DU loads select your hard drive entry (mfgr.'s ID and drive size) from the the left side list. In the DU status area you will see an entry for the S.M.A.R.T. status of the hard drive. If it does not say "Verified" then the hard drive is failing or failed. (SMART status is not reported on external Firewire or USB drives.) If the drive is "Verified" then select your OS X volume from the list on the left (sub-entry below the drive entry,) click on the First Aid tab, then click on the Repair Disk button. If DU reports any errors that have been fixed, then re-run Repair Disk until no errors are reported. If no errors are reported click on the Repair Permissions button. Wait until the operation completes, then quit DU and return to the installer.

Reinstall OS X: Snow Leopard's installer will not erase your hard drive and will preserve all your data, users, network preferences, and third-party applications and their support files.

If DU reports errors it cannot fix, then you will need Disk Warrior and/or Tech Tool Pro to repair the drive. If you don't have either of them or if neither of them can fix the drive, then you will need to reformat the drive and reinstall OS X.

I have seen this before. It seems to be a bug.

Try logging in to the new admin account, and entering the following in Terminal (where "daughter" is your daughter's account short name.) It should remove your daughter's account from the admin group.

sudo dscl . -delete /Groups/admin GroupMembership daughter

enter the new admin account's password when prompted, and press return.

Oh, that's a problem. You cannot use the "$" character in a username. It's a special character used as a wildcard in Unix. Also, I've found that sometimes Unix objects to using "admin" as a username since that is also used as a group name.

I suggest you boot into your account and delete that account. Create a new account for your daughter and this time use a normal username like you have for your account.

"admin" can be used as a username; the only admin account on my Mac has exactly that user name.

But if one chooses to use "admin" as a username, it can only be an admin account. It's not possible to remove the "admin" user from the admin group. OS X warns about this if one tries to create a new user with the name "admin".

I agree with Kappy. Delete the account and make a new one.