Probably fine for child abuse porn in a drawn style, like loli, but probably not sufficient for the photorealistic porn that it is supposedly intended to replace.
This is ultimately the flaw in your argument that an AI can produce “new” works because it doesn’t need to have seen a toddler riding a lion on the moon to be able to produce that image. If you didn’t give AI photos of lions, it would never be able to create a lion. If you never gave it photos of toddlers, it would never be able to do a picture of a toddler. And if there were no photos of the moon in its training data, it would be incapable of producing the moon. It cannot create things it has not seen. It can only arrange things it has seen in combinations that may or may not have been previously thought of (with billions of images in the training data, you can’t say there isn’t a Photoshopped photo of a toddler on the moon in there.)
Without actual child porn in its training data, it would never be able to produce any, because even when it’s capable of piecing individual elements together into a “new” piece (basically an advanced collage), if there’s no images of children being abused in the training data, it’s not going to be able to piece it together by putting a child’s head on an adult’s naked body, and result in anything that’s more satisfactory for paedophiles than actual photos of children. There is therefore no ethical means of producing AI-generated child porn, and therefore it is not an ethical alternative. Somewhere in the chain, there are still children being abused.