Gym etiquette, unaccompanied minors?

At the gym where I lift, lately there have been these two teenage boys (they look about 13/14 years old) who have been coming in to lift. They clearly don't know anything, they bounce around from one lift to another with no plan, which I don't really care about. The other day they were messing around cleaning fixed weight bars, and every time the one takes the bar off of the ground, he rounds his back about as far as humanly possible and jerks it upward (cringe). They've done several other things with poor form, but nothing stands out as dangerous quite like this.

Now if these were adults, I wouldn't even give it a second though. Adults have every resource in the world available to them in order to learn what they need to know, and if an adult does something stupid and hurts himself, well he's an adult, he should know better. But these are stupid kids, unsupervised, who clearly know nothing. Do you leave them alone? Politely point out the danger in what they're doing wrong? Point it out to someone who works at the gym?