Well, first of all, you theoretically shouldn't run into anyone younger than 21 in a bar if you're in the US.
Kids also "date" each other at ages younger than 18 too (which is obvious)... what they actually do while dating is another issue, and I think you've hit on that adequately, Flaser (the 17-year-old dating a 15-year-old situations sounds like it was blown out of proportions to me). To add to your query, though, I do not feel reverting to "Romeo and Juliet" romanticism should be an option in the modern age. Someone who's 14-16 should probably not be involved in intimate sexual activity. That IS a question of moral and social ethics, though, and adapts with the culture as a whole. "Dat's it."
I've never actually heard of cases where an individual was charged for distributing images of themselves. Granted, you should question their motives, but placing charges on those individuals seems rather "grey" in nature. I don't approve of the actions of those children, but they simultaneously are children. I'm not quite sure there's an ideal ruling for such things.
The "suggestive artwork" issue is a new one to me as well. Despite its questionable morals (and the morals of those who employ it), it is art. As far as US rulings go, that should be protected via the First Amendment of the Bill of Rights. AND AS SUCH, it shouldn't be a problem. If you state that such might be an "enabler for foul acts," then I combat that with this: How many people got riled up over a book and did something (not necessarily bad) because of it? The principle is thus this: If you're sick, you're sick. If you're nuts, you're nuts. If you're that messed up to act on things such as literature, games, or in this case, animation, then you're going to cause a problem regardless. Now, that's not to say you might take in poor ethos from the smut you're viewing, but that is an issue of personal morals. If you have any decency, you probably won't find yourself using that media anyway. In conclusion, it should have no legal restrictions apart from whatever is used to regulate ratings for viewers/buyers, etc.
If you're producing or supporting the CP industry, then I have no qualms about beating you down with the book. :ma-Thaeris