Why would child pornography laws have anything to do with someone pretending to be under-18?

That's distasteful, sure, but objectively, people over-18 are not children.

Basic recordkeeping laws should make it easy to ensure that everyone involved is of age, even if they're sucking on a pacifier, wearing a diaper, and saying "goo goo ga ga".

> have anything to do with someone pretending to be under-18?

CP statutes also deal with "simulations" of underage participants.