So you outsource your parenting to the police and the courts?
I absolutely agree that you have a right to control the influences in your kids' lives (to some extent, at least). But why do you need to involve the law in this way?
Say your daughter receives a lewd photo from an underage male. Now she's in possession of child porn (whether she wanted the photo or not) and could end up on a sex offender registry for life. How is that sane?
And the guy who sent her the picture is "trafficking in child pornography"? C'mon. That's ridiculous.
Many of these crimes are on the book with "strict liability"; that is, the mere fact of existence or possession triggers culpability, and intent doesn't enter into the equation.
I think the better model is in places where the age of consent is at some reasonable age below the age of majority (no, I don't have a good definition for "reasonable", but that doesn't mean we shouldn't try), as it is in many places. There are no legal ramifications of sexual behavior down to that age, but parents are, as always, free to set limits and impose consequences if they aren't obeyed.