I'd probably cut both the kid and the parents some slack. Far more infuriating to me is adults who talk through a performance. I find this disrespectful not only to the artist but to those who've come to see and hear and maybe even participate. On numerous occasions I've voiced the fact that I came to enjoy a performance to chatters nearby and asked them to either quiet down or take their conversations elsewhere. Some stare at me as if I'm a creature from outer space, but it seems to work.