My son is 5 and is the same way. I don't think it has to do with anything we have done or not done though. I think he just realized that as he gets older he has more school time and less play time, less time with mommy, and more responsibilities. He fairly often freaks out at night before bed about death and wishing he could be a little kid or a baby. Sometimes the freak out is about me dying. I guess we just have very aware kids. I read a mr. Rogers website about talking to kids about this and then explained to him how there are tons of people who love him and would never leave him alone even if I died or even if he was an adult or even if he didn't know how to drive and that seemed to help the last time. Other than that I just help him find happier thoughts when he gets this kind of anxiety. There's not much to say about growing up and death... It stinks but we can't change it, so trying not to dwell on it is really the best we can teach them I guess. Good luck!
