I upvoted you, since I think it's a fair question :)

I may be miss reading it, but it is probably not meant to be condescending - They are noticing someone's behavior and use a commonly understood proverbial phrase or idiom to describe it. In this case "gang of condescending children" might have been better stated as "childish attitude and groupthink" as it is meant to portray them as behaving with mentality of elitism that feeds off other people around them who echo and embolden their thoughts, making it very easy for them to dismiss others and their views unilaterally instead of reasoned and compassionate objective reasoning.

This statement might also be used like this - "So when Billy and his friends came back to town from their freshman semester and humanities 101, they were all too eager, like a gang of condescending children, to argue with Billy's WW2 veteran grandpa about how wrong he was about how the world worked and how much more they knew about it."