Knowing what a nude adult looks like doesn't mean that the model knows what a nude child looks like. I'm quite sure it's easy to generate disturbing images like that, but actual paedophiles I think won't be satisfied with child faces on small adult bodies.
Ordinary deepfakes actually have a very similar problem: Sure you can take a picture of a celebrity and tell the AI to undress them -- but it won't be their actual body. The AI is going to be able to approximate their overall build but it's going to be a generic adult body, not the celebrity's body. Or, differently put, AI models aren't any better at undressing people with their eyes than teenagers.