You can restrict access to Google Fiber TV apps, such as Netflix and VUDU, using the same parental controls you use to restrict other Google Fiber TV content.
Set up parental controls according to the instructions in Set up parental controls.
On step 3, when you specify the types of content to restrict, select Restrict Access to TV Box Apps on the bottom left under Other.
When you set this restriction, anyone who wants to access any Google Fiber TV app has to enter the parental lock code. Without the parental lock code, you cannot access those apps.