It occurs to me that John and Elly's expectation that their children somehow know people that they do without their actually having to tell them who said strangers are is part of a wider problem in the way that they see the world. There's a pretty good clue as to what the problem is when Mike gets hectored about wanting to not be steamrolled into a display of filial piety from his loutish adversary Brad Luggsworth. What seems to be going on is that John and Elly tend to not WANT to understand that their children have problems that do not relate to them. The same impulse that refuses to allow for the possibility that the kids simply don't know the same people they do blinds them to the fact that their peers loom as large in the kids' lives as they do. Given their generation's tendency towards a smug and self-righteous lack of curiosity and sheer dimwitted boomer hypocrisy, we can expect any number of pointless verbal aggression directed at the kids because Elly and John don't know who their kids' friends are and should not be expected to learn either.