Did you ask the doctor why? If your sons mind is at the equivalent to a 6 year old, the doctor may not think fmla is a good thing for him. Speaking from experience of someone I knew in a car accident that injured their brain and basically was a child in development again. Working maybe the best chance for your son to regain mental stability again. Like my friend, the rehabilitation was using there brain with challenges much as possible. There's a lot of reasons why the doc may do this. As for FMLA, it's really up to the doctor.