This paper reports the results of two dual surveys of children from Primary 4 through Secondary 3 and their parents, conducted between November 2011–January 2012 and September–October 2013 in Hong Kong. One key finding, which confirms those reported from other parts of the world, is that happiness declines as children grow into their teens. The present study discovers that this is related to declines in love, insight, fortitude and engagement: four aspects of mental capital essential to happiness, which may be associated with mounting pressures as children grow up. Pressures from extracurricular activities surprisingly appear to have a much greater adverse effect on happiness than pressures from school work. These results may reflect the fact that a child's disposable time decreases monotonically as they grow older through age 13, with extracurricular activities aggravating the lack of leisure. Perceived financial well-being of the household is found to be associated with children's happiness and children's love scores. A loving relationship between the parents and their respect for the child's opinions and privacy mitigate any intergenerational barrier to effective communication or negative effect from parents’ age, and enhance happiness.