I think we are missing a couple things.

First thing though is yes it is entirely reasonable. Most kids mature at different rates. SO yeah at 6 depending on a lot of things a kid think that. Who know this could be one of those things that causes the kid to develop further along.

But, what you neglect to tell us is what happen in said manuscript that causes the child to think this. I mean what would you say, if I asked, "'Is it reasonable to a child could think he could see dead people.... after watching a movie?"

I mean, within the context of the movie it is entirely possible given what goes on in that setting. So we need to know what's going on in the setting.