BlueDingo said:
I think he meant this, and I'm pretty sure fictional children still count as children just as fictional dogs still count as dogs.

U.S. law has tried several times to ban fictional underage erotica and has, surprisingly, been successfully challenged and pushed back every time.

This is courtesy of the obscenity principle - but underage erotica is probably way more likely to be found by a jury to be obscene, compared to erotica of only adult characters, all other factors unchanged.