That is a real problem but for an unreal situation. Nobody is advocating that we combine (A) a child-safe browser with (B) a completely unlocked device in every other way.

When I buy/configure a device which prevents Little Timmy from viewing smut, that device is also going to have a parental code for installing new apps. If that part is left open, then Little Timmy wouldn't have to even bother getting a different browser, he could just install direct porn apps.

> But it needs to be at least, like, 60% perfect, right?

That can easily be reached by ensuring that child-mode covers default browsers and also the ability to install a new browser. If Little Timmy is turning on debugging over USB to sideload, then a fundamentally different parenting strategy is required.