What you should do, they'll explain, is pre-register your schemes with the Commission, before you do anything. Then, the commission can figure all the harms that would result, if you did that as described, and what your likely sentence would be if caught, and suggest ways you could work together and make it not as bad. In exchange they can offer a significantly reduced sentence if caught, and sometimes even direct cash to make working with them worth your time, too.

Not all of this only applies to criminals, there are some socially agreed upon standard practices that affect everyone. For example?

Oh yeah, I'm supposed to tell them about that too.

Now that you're old enough to hopefully understand this sort of stuff, you should also know that, if anyone ever shoots you with a paintball gun while out in public, society expects you to lie on the floor and play dead for ten minutes or until the situation is over. Also you're not allowed to, for example, try to tell the guards where the gunman went, or stop the gunman from grabbing your wallet, or anything like that. If you get personally robbed in any situation like that the Harms Commission will almost always just compensate you later anyway. 

Afterwards, you're prohibited from testifying against anyone about anything prior to when you got shot, if the guy who shot you doesn't want you testifying about it. That sounds weird, but remember that if society didn't agree to that standard, people like me would just shoot witnesses with actual guns and then they still can't testify against us and also they're dead.

If you really strongly don't like the idea of having to do that, you can fill in this form with the Commission and they'll try pretty hard, to the extent it's possible, to make sure that you're not around when crimes are scheduled to happen. From my experience most people think it's pretty fun, though.

As for the bad guys side, if you do a robbery and then shoot a bunch of witnesses with a gun, you'll be charged with robbery and mass murder, and probably spend the rest of your life in a maximum security cell. If you use a paintball gun instead, you're not actually guilty of murder, just robbery, and you can't get more than 10 years in a medium security apartment for only property crimes.

If you don't get caught, which isn't easy but they still can't testify against you and the guard would have spent way more resources hunting an actual murderer, then you get to keep all the profits just like you would've otherwise.

I've personally killed over a hundred witnesses, and since nobody saw me do a crime and lived to tell the tale, I'm still out here free.

Why is everyone letting this moustache-twirling supervillain talk to us kids, exactly?

Many political factions convincingly demonstrated that they could, if they wanted, migrate to cities dominated by their own faction members, raise their children in a culture of their own propaganda, and produce faithful faction members out of a supermajority of children. This would then turn politics into a race to the bottom of who could mass-produce the most brainwashed children to control elections, until a faction got a majority and could convincingly demonstrate it could take over the world by force if everyone else didn't just capitulate first.

Since most factions would prefer to avoid that race to the bottom, it was compromised that all factions would forfeit the right to do that, or else be ganged up on by everyone else.

The compromise agreed is that all children get exposure to representatives of all political factions, mostly in proportion to voter support and with relatively few other constraints.

Some people vote for the crime faction, so they get a turn at trying to brainwash children into their ideology, too. If you stop applying the rules of fairness to people just because you don't like them, you were never really applying the rule of fairness in the first place.

Wouldn't a supermajority of factions at least be willing to gang up on the faction explicitly in favour of crime?

If they'd be going to do that, the sort of people in favour of crime would stop calling themselves a "political faction", and start just shooting everyone they didn't like. Who's to say who'd be left standing at the end of that, the guys who believe in following the rules, or the guys who have repeatedly made nuclear weapons in their own basements?

If you stop applying the rules of fairness to people just because you don't like them, you get to play out the rules of nature, instead.

Tiger will, on behalf of her conspiracy, turn over their plans.

If you do this with an actual gun, it'll count as lethal violence and they're not just going to release you when you start claiming to not be a child anymore.

Actual murder gets taken very seriously.

But if, hypothetically, I did it with a paintball gun?

We feel you're not acting in accordance with the spirit of harm-reduction, if you were never willing to do the non-harm-reduced version of your own crimes. It seems unlikely that you'd still be planning to do this if you didn't know you could bargain away having to do any actual violence, and remove any risk of real consequences at the same time and just get it all suppressed at adolescence.

That's an interesting theory you've got there. Maybe you're really confident in it. Maybe you're 99.5% certain. If that were the case, by refusing to bargain, you'd expect to be stopping 199 robberies, and causing 1 mass murder.

Do you think that's worth it?

… If we went along with this, would you later be willing to consent to what you've said here being used as evidence in parliament for lowering the minimum age at which the courts will start treating people as adults against their will?

Objection! That’s corruption. The Harms department guy is using his public office to create evidence that supports his political faction. If public office powers are going to be used in that way, we’d have to ensure they were fairly split between factions too, and apparently one of the factions is pro-crime so that’d be a nightmare.

Objection Sustained. That last guy shall be thrown into a pit of angry lions for misconduct.

Anyway:

... I've been led to believe that nothing I say to you can be used as evidence for anything.

Not without your permission, no. We wouldn't dream of anything you say here being used as evidence of your guilt, nor as evidence of anything else without your consent. It can totally be used as evidence of your innocence, if you're somehow accused of something that the Harms Commission knows you didn't do.

... huh.

Sure.

Anyway, if that's all agreeable, I'd also like to pre-register this other thing too, and I've been led to believe that even though you can't say anything that would help me, you can provide legal advice about whether or not certain things are crimes or whether certain legal arguments would work?

Yes, we are also lawyers. We can, technically, give that sort of legal advice.
Strictly so long as none of it is helpful.

The first actually hard part is getting a firearm.

You'd think nobody would be willing to sell guns to children. It's a pretty law-abiding society, mostly.

Earlier:

Here's proof we can flood the black markets with cheap handguns, if we want to. Here's how hard it'd be for people to buy those guns. Here's how much profit we expect we can make before you found our secret factory.

How about you try flooding the markets with paintball guns instead, and we use that as a baseline for how many sales you could've gotten before the guards stop you?

Objection! They're only interested in sales-revenue, right? So the Harms Commission would be doing a way better job if people didn't even get paintball guns out of it, and they just bought out their supplies until the guards caught them.

Maybe society thought about paying them for that outcome, and maybe my friends and I offered to pay them even more not to do that?