Parental controls on YouTube?

My cousin ended up on an explicit video on YouTube. We need to find a way to put parental controls on YouTube, without blocking or turning the app off. As once the password is entered, those videos could still be viewed. I know how to do this on the Internet on PCs and Macs (laptops and computers) but for some reason the opotion is not presented in the app. As I said, we do not want to block or turn off the app, and even if we downloaded one of the web servers for "safe browsing" as far as I am aware of, it would not affect the other apps. Help would be greatly appreciated.