That's as likely to be effective as the famous "To use Bebo/Facebook/Twitter you must be over 13. Are you over 13? [Yes] [No]" option.

"To get the thing you want, you have to say Yes. Will you say yes?" - How many people honestly choose the "no" option?

We have facial recognition technology that recognises black people as gorillas, and other face recognition technology that ignores black people.

Nudity recognition is going to be really hard to detect.

Since these children were using "vault apps" those vault apps would probably start to include bypass techniques.

And this ignores the sexual health stuff that children can validly search for. You don't want to block images of how to check your testicles for cancer, for example. (Although photographs are probably not helpful blocking the images would be counterproductive.)

The last one at least wouldn't apply. Only pictures the phone takes would be blocked. Assuming this is some sort of OS/Administrative app, I doubt the vault apps could get around anything preventing the camera service from returning an image without, basically, rooting the phone. Other than that, the facial recognition stuff is a fair point.

Wouldn't it be relatively easy to have each citizen enter their passport number upon setting up the phone, and then do natural language processing so the phone would just block the transmission of any forbidden speech unless the owner held a diplomatic passport? Of course, technology can be circumvented but this would be a start.