It takes a certain kind of nerdy kid to sit down and watch a documentary (not judging, I was that certain kind of nerdy kid). With video games, the user, i.e. child is actively engaged. Video games require more from the consumer. I found myself much more likely to dig into history while playing civilization than I did while watching a documentary for example.
Actively engaged does not mean exercising higher cognitive function, and even less so developing higher cognitive function.
Imagine if e.g. basketball players never practiced but just played for all the marbles at the most competitive level every day when they stepped on the court. You would have chaos and exhausted players.
