 So in England, in February of this year, two mothers were talking at the school gate after they dropped off their 11-year-old kids. Both of them were alarmed by the number of 11-year-olds owning smartphones and by the sort of research on childhood anxiety and depression that had disturbed Jonathan Haidt. The mothers were specifically upset by what they called scientific evidence revealing that the younger a child is when they get a mobile phone, the higher their incidence of mental illness is.