Not all children had a happy childhood. Some of the great genius in art also suffered from mental disorders. It was not necessary so that the mental disorder helped them to be great, it could have been like when they had to spend so much time alone they were "forced" to develop something.
" artists who suffered from a mental illness – and how it affected their art.
I agree with Diane Sunar . Divisions activate stereotypes and they decrease the complexity inside the world. I would like to add that being happy could be related not to every single context and essential dimension of our life. For example, work can be connotated by emotions like happiness, but the family could be perceived as extremely negative. However, I believe that in the two categories that you mentioned, mad and child, there is a point in common. They can perceive and be subjected to fewer constraints derived from the process of socialization; they are less involved with respect to social practices and rules.