The first part of the linked article basically seems to imply that the military is developing games that covertly brainwash kids into soldiers. DARPA has no reason to fund anything like that. We're Americans, our culture does that for free!
Two thirds of the way through, it dispenses with that unstated pretext and makes itself about the military and Federal government's overreach into American educational institutions, which is an excellent point that I can get behind. I wish the author had dispensed with the conspiracy theory undertones and gotten to the point from the get-go.
DARPA wants a better way to train soldiers, so it went to this CGS place to develop advanced tutoring algorithms. Since these algorithms have a wide variety of use-cases and CGS is more used to working with kids than soldiers, they developed them around teaching STEM skills to kids. That's dubious in a "this should be funded by a different branch of the government" kind of way, but it's not Ender's Game, it's not the SPARTAN program, and it's not Polybius. I'm not saying our government would never, ever do anything like that, but that's not what's happening here.