SAD is a form of depression....I too suffer from it. Is fairly common among people who suffer from depression and occurs during the winter when the weather is dreary and cold, and this type of weather usually contributes to staying inside a lot rather than getting out and being active. As a health care professional, I've never heared of it being related to broken bones, unless your son is deliberately breaking his bones because of depression. But if you are asking if the lack of sunlight is causing his broken bones, most likely not. I'm assuming he eats balanced meals and is not seriously suffering from malnutrition or other disorders. It is however, unusual for children to actually suffer from SAD but not unheard of. You might look for other causes for his sadness and try to determine if it's intermittent or constant. If intermittent, then's it's probably due to situational circumstances, but if constant, he might need light therapy or a therapist to determine what is causing his depression.