My 4 yr old has become concerned about mummy, daddy, nan, grandad dying. Not soon or prematurely just at all. I've explained and reassured over and over that we are going nowhere, even dad's mummy and daddy are both still alive and daddy is very very old so while everyone dies eventually he (DS) will be unimaginably old, older even than daddy, before he will have to worry about it. What more can I do?