I expect any porn model trained on a sufficient diversity of adult actors could be used to make convincing CP even without having it in the training data.

I know I’m wading into the danger zone here, but let’s also remember we’re talking about teenagers. A (for example) 15 year old’s body type will be closer to an 18 year old’s than a 5 year old’s, so the perfectly legal porn model would work just fine for that, uh, purpose.