Former bureaucrat in a certain state's Dept of Corrections here. Thus, with those bona fides you can trust my response. (Really, trust me on this one.)
Your 7-year old nephew is not a gang leader - yet. The issue of learning cooperation and leader- follower-ship relates to gang activity only for those who did not learn all the rules while they were still not recidivists in the juvenile/adult correctional systems. The innocent youth of today (which we will for the moment presume includes your nephew) merely learn skills which enhance their membership in the Borg by playing games such as D&D or football or other team sports, as all of those have "others" who are not directly involved in the playing of the game who oversee and control the actions of the gamefield "leaders". They may be called coaches, or teachers, or Mayor, or Congressman/Senator, or even President. But you can be sure that there is someone watching over their every move, ready to step in and correct any improper behavior.
Gangs, on the other hand, do not select their leaders and position them out of the direct line of play. Gang leaders assume the position (Hey! There's a pun there. Laugh, darn you!) by overcoming all the other members and physically and mentally dominating them in order to maintain the position of gang leader. That is why gang leaders are so dangerous in prisons - they do not listen to and obey the orders of the hidden overlords and their minions.
Well, there's also the real fear that some of the maps that get drawn in D&D games might turn out to be escape maps. I'm serious - I've heard that said by some very high up the foodchain officials as well as by some of the line staff.
Now, depnding of the laws of your state/locality, your nephew might still be a gang member if he regularly associates with somewhere between "three or more" and "five or more" individuals who come together regularly for the purpose of violating the law. You know, activities like playing WH when he's supposed to be doing his homework or cleaning his room, or staying up past his bedtime. If that's the case, you can take comfort in the fact that there are several federal law enforcement grants out there that provide money to the local law enforcement agencies to provide rewards for turning in names of gang members.
So rest easy. Either your nephew is not yet a gang leader and might, if he follows orders well, never become one. Or he really already is and you can get rich by turning him in. Win-Win, wither way.
stay safe.
