As i child i used to get them alot too. generally reoccuring nightmares.. I had one about this volcano in lanzarotte that kept killing me and my nana...

I think as a child you might get reouccouring dreams because you do not have that much life experiance.. and when you experiance or see something that inspires and intense emotoinal response then in manifests itself within your dreams. You haven't anything else that feels like that so it keeps attacking you with the same one over and over...

where as by the time ur about 12-15 you have seen so many movies with differant ways to be killed and might have traveled a bit more and seen and done things.. so that the dreams do not occour as often.. Fear can manifest itself in a number of ways instead of just the few you knew as a young child.

Well its an idea...