Collin...my little thinker

Collin is my child who has tons and tons of questions, thinks alot, dreams alot and is very excitable. This is wonderful in so many ways, but it also has a downside. Lately, he is obssessed with the concept of dying, what happens when you die, when is he going to die and a fear of dying. This has been so hard for me. I always try to be as honest as possible with my children, but of course, on his level. So, over Spring Break, I hear him crying at night and go to him. He is sobbing and telling me, "I don't want to die". I tell him, "you don't need to worry about that, that is 1 million night-nights away". He asks, "Will I come back alive after I die?" I just didn't have the heart to say "No", so I asked him, "do you want to?" He answered, "yes" and so I just left it at that. I have a policy that I do not believe in lying to my children, but I didn't want him to be more fearful and worry. I went on to explain that when we die, we go to heaven. Heaven is perfect and wonderful, there will be no more boo-boo's, everyone is kind, and you will be with all the people who love you so much. We prayed and he seemed to calm down, but I just felt so sorry for him.
The next morning at breakfast, he asked the girls (Reese, Ashton & Arabella), are yall scared to die? They said COL-LIN!!! They didn't give much more of a response than that.
THEN, the other night I was tucking him in and he said, "Mommy, I don't want you to die" and I said, "Collin, I am not going to die for a really long time, you don't need to worry." After discussing the last couple of incidents with friends, one of them suggested trying to get him to visualize and define heaven. So, I asked him, "what do you think heaven looks like?" He said, "a really scary place." I then tried to once again explain the pleasantries and perfection of heaven and tried to get him to participate. I am hoping we can find some peace with this soon. I am trying to find some good books, from the Christian perspective on dying, that are on his level, so if you have a good one you recommend, let me know!