For the past 70 years, scientists in Britain have been studying thousands of children through their lives to find out why some end up happy and healthy while others struggle. Today it's the longest-running study of human development in the world, and it's produced some of the best-studied people on the planet while changing the way we live, learn and parent. Reviewing this remarkable research, science journalist Helen Pearson shares some important findings and simple truths about life and good parenting.