Instructions
Make sure the Wii is properly plugged in and working, then switch the power on. The Wii Channel Menu should pop up after a Health and Safety warning.
Choose "A" on your Wii remote when you see the Health and Safety warning then proceed to the Wii Channel Menu and look to the lower left. Press "A" again to make your cursor appear (it looks like a hand). Your cursor hovers over the Wii Menu button.
Look for the Wii Settings button in the Wii Menu. It has a wrench on it. This leads to some of the Wii's main settings such as screen resolution, sensor bar placement and passwords.
Select System Settings in Wii Settings by holding your cursor over it and pressing "A." then press the plus button on your Wii remote. The top option should be Parental Controls. Click it and say "yes" to the question it asks you.
Enter a four digit PIN code as restriction enforcement, but make sure not to tell anyone what it is, or else they might get through the parental block. You might want to jot it down and put the password in a safe place in case you forget it in the future.