I think there's a lot of nuance in these kinds of situations, including that it seems unlikely that memory loss of this kind in a child this age would be only caused by the psychological trauma of losing his/her parents (and, perhaps, witnessing the parents' terrible injuries if the child was in the car. If the child was in the car and had some head trauma, it may be that the head trauma caused the amnesia. Long term memory isn't usually affected in this kind of complete way by psychological trauma, so it would be a very unique situation if this was the result and the child wasn't in the car and/or injured.

The other thing that strikes me is that foster care in these kinds of situations would have counselors working with this child, getting some of their things from their house, using pictures to talk about the child's parents, visiting with the parents, etc. But that is in this day and age and in communities with the proper resources. So part of the problem for a child in this scenario is the response from others in the face of the loss of the parents; if just ignored and "call us mommy and daddy" is all that was done, it would be adaptive and smart for a child to do exactly that. So if the adults around are pretending, the child is going to pretend (and have memory loss).

I think there is something in the literature on childhood trauma that suggests it is not just the trauma itself but how the world around the child reacts to it that either facilitates healing or makes it worse for the child (or perhaps both in different kinds of ways). I know that was true for me, when I *thought* I told other people and they just blew me off, the despair of not being believed or helped was pretty terrible. Looking back I think that I was not terribly clear or I more wished that I had told others, but it may also be true that people were not able to hear me, not because of anything wrong with me but because of the time and the situation.

It's an interesting question, how big a deal is ___ ? I don't know if what I've written is necessarily responsive to that per se. To me the more important piece is how did this thing, no matter what its size, have an impact?