It's not the imagination - most kids have that - it's the fact that it appears to have got him into its grip, into a negative place that he doesn't seem able to control. Or else, that it might be masking some troubling real event that the boy can't communicate directly. That's all I've been trying to get across. It's not a good idea to dismiss unusual behaviour in a child as "just imagination" and not investigate further. And that grieving and guilt DOES sound unusual: if he invented it, why can't he simply un-invent it? I think that should be looked into.

Maybe imagination is all it is. But I'm not convinced anyone in that family knows for sure.