In these cases, most people are upset that an infant lied. They might argue that the adult reaped the consequences of a bad act by the infant (the lie).

I would argue that an adult is being punished not for the infant's lie, but for his/her own unreasonable failure to verify the age of the infant before proceeding to have sex with him/her.

Statutory rape is a strict liability offense. That means that a person can commit the offense, regardless of whether or not they intended to. If the facts state one party was underage, the adult commits the offense, regardless of knowledge, intention, or or any other factor.

In that situation, there is an implied affirmative duty to verify ages before you have sex. It's just common sense. If you can commit an offense by virtue of not knowing a fact, then most reasonable, law-abiding people will sure are hell want to verify the facts so they can't be caught with their pants down later on and suffer very harsh consequences. Affirmative duties are special, because you have to perform that duty regardless of what the other party does. In other words, the lie is really irrelevant to the punishment, because it doesn't make the duty to verify go away.

But, let's move on from that point. Let's talk about the lie. What could the minor be charged with? People might suggest: Fraud, or fraudulent misrepresentation.

Well, fraud and fraudulent misrepresentation will vary between states. For the sake of having a concrete example, let's look at what Oregon considers fraud or fraudulent misrepresentation: a lie, to obtain a benefit.

This is usually interpreted within the realm of contract law. So, that means: fraudulent misrepresentation of age to obtain material benefits like loans, cars, services, whatever. Interpersonal services? Those aren't really quantifiable. I don't know what benefit it is to me (or detraction it is to you) for me to obtain your sexual services, unless, of course, you're in that professional work and we're signing a contract for it. Then it becomes kinda like me misrepresenting my age to get you to sign a contract to paint my house, trim my hedge, or perform any other service.

But wait! If you look at the bottom of the page under subsection 4, it explicitly carves out an exception for liquor sales. Why? Because there's an affirmative obligation for liquor salespersons to check ages, much like there is a (sometimes unspoken) obligation for adults having sex to be proactive about checking ages. So, the services argument wouldn't really work out after all, either.

Okay, let's go one step further, and pretend that limitation isn't there. Let's pretend we could charge children with fraudulent misrepresentation of their age to obtain sex from adults. What then?

Well, look at the benefit: you could stop children from lying, by punishing lies.

Look at the drawbacks: you place a big hurdle for already vulnerable parties to prove in court that they were in fact abused or harmed by more powerful parties. You also give some abusive adults an additional tool to further harm their infant victims.

If you weigh the outcomes, I think it's preferable for an innocent adult to shoulder the burden of checking a piece of paper or photo ID before having sex with someone who appears to be a minor. It's not an unreasonable burden, given the alternative: countless child victims being victimized through the legal system that gives adult sexual abusers a tool for their defense.