How do I reset parental controls on a Wii system?

You can go online and get a reset code.

Basically, when changing parental controls, the first thing you need to do is make sure that the date is correct on your system (I believe this is for logging reports, potentially). You can then use the "I forgot" option when asking for a PIN/Security question in the Parental Controls section. This will give you an ID number for your Wii.

Go to this address, enter the code, then it will give you a pin that you can then use to unlock Parental Controls.