A six year old child that is scared going to his room just after, or shortly before sunset.?

Until 2 months ago, our son would brush his teeth, and go to bed without any problems. A mother of one his clmates ped at that time, and school had a conversation about death. For few days he would ask hundred questions about death related stuff. It was about then that he is scared even before sunset. We have told him that it is okay to be scared and that we were and are scared of some things, that we are healthy and strong..., but things are not getting better. He is a very smart and wonderful boy. He is loved, but not spoiled. Any ideas?