There is a question to ask here
Do we want to prevent any form of exploitation of children?
Do we want to prevent any form of enjoyment of sexual pleasure from perceiving information that is perceived by anyone else as representing children?
The first is clear and easy to concretely describe.
Laws prohibiting the first relatively are easy to frame with little risk of unintended consequences.
Laws prohibiting the second are open to almost infinite feature creep and framing laws for this are almost certainly going to have unintended consequences.
Digitally aging images of a missing child so that they can be identified years after they disappeared has been used to digitally reverse aging of adult entertainers to produce what appears to be child pornography.
No children exploited here. This has been around for years.
Drawing cartoons of children to produce what appears to be child pornography. There are lots of artist that can draw a picture of what looks like a child without needing a child as a model.
No children exploited here. This has been around for millennia. I am sure there were a few statues in the Grecian Empire of individuals we would identify as underage without the carver needing to use a model.
Drawing a cartoon of a bandicoot or a fox with a flying tail of an indeterminate age, but looks like the character in popular children's entertainment might be identifiable as something that can be experienced as child pornography.
No children exploited here, though there might be some copyright infringement. There is a surprising amount of such content available.
Creating a customizable doll.
Lots of dolls and action figures with bendable and pose-able limbs.
Lots of dolls/action figures that can have their configurations changeable. Mr and Mrs Potato Head.
Lots of dolls/action figures that can simulate a number of biological behaviours.
Wetting themselves, sucking on a bottle, crawling, walking, speaking phrases, speaking context aware phrases, full on human language interface.
Writing a story about suck a customizable doll/action figure.
Drawing a cartoon or creating animation about such a doll/action figure. Astro Boy.
Creating Pornography about such a doll/action figure that that is brand new from complete cloth.
There is no child exploitation here, but there is an almost infinite variety of pornography that can be imagined and produced.
The doll/action figure/android/robot does not even have to look human for someone to perceive them as something that is recognizable as a child.
There is simply no limit on what can be objectionable just as there is no limit on what people are capable of enjoying.
There are an indefinite variety and indefinite count of individual that are capable of enjoying experiences that can be achieved through various forms of child exploitation. The only reason it is not infinite is that the population itself is not infinite.
This does not mean that these individuals necessarily need to exploit any children directly to enjoy these experiences.
Distracting ourselves by trying to detect, track, legislate against, prosecute, incarcerate all of these various types of people and activities will dilute our focus on protecting children in our care (that's all of them)
Going after this infinite variety of people is low hanging fruit for legislators and law enforcement bodies. It allows them to crow from the rooftops that they are working hard to protect everyone from everyone else that can outrage and infinite variety of outrages. They can do this using easily applied technical tools to track and trace and spy on everyone.
Focus on the hard work of protecting children directly instead of sticky beaking on everyone in the hope of finding something that outrages someone.