Well, I guess I didn't put a scholarly amount of thought into it... but...

Morally wrong: because the law is against it, it could potentially harm a child to have sex with an adult. Not because of the act itself, but because of what the authorities will do to that child (brutal questioning) and then to the "perpetrator", which would in turn affect the child who cares about that man.

Spiritually ok: because we are freed from the Law (not the law, but maybe there is a connection) in Christ. We are to obey the spirit of the Law, rather than the letter. The spirit of the law (lowercase intentional) is to protect children. Fully responsible and caring adults having sex with children (and by sex, I'm assuming it's at an age appropriate level without physical harm of any kind) and unceasingly displaying Godly love at the same time would not be sinning, and would definitely be protecting that child to the best of their ability. If the authorities came in, that would not be the fault of the man involved, because he was still trying to obey the spirit of the law.

I'm not sure if that ramble made any sense at all. I could be totally off my rocker.

At any rate, those "spiritual" examples are completely hypothetical and possibly unrealistic. The important thing "morally" is that the risk is too huge and it just shouldn't be done. That has nothing to do with whether or not it is sinful, I'm speaking practically here.