It's their home life, stupid.

Children cite family conflict as main cause of unhappiness
Family conflict is the biggest factor in causing unhappiness among children, according to a survey by The Children's Society involving around 7,000 10- to 15-year-olds. The charity asked children how different aspects of their life affected their happiness.

The survey found that seven per cent of children were significantly unhappy. Family arguments were the biggest determining factor, while the structure of families made a negligible impact on children’s sense of wellbeing.