I improvised the plot, from nothing at all and some vision cards picked up almost at random, which is not an unusual way for me to run a game. I thought he'd go for someone with a big sword. I don't know any other kids who'd know the background. I may try again. The ease with which children do it, and the problems I have dealing with it with them, is one of the reasons I am suspicious of the Theatrix paradigm.
Children do it with ease, fluidity and no problem with consistency.
You can go with it on minor details, but it can ruin the plot - worse, it can ruin consistency and the reality of the world. Children don't have inhibitions on their imagination. I sometimes wonder if I am stifling Sasha's creativity by roleplaying with him - channeling it into structured play rather than wild play. That's not all that different from what I get out of roleplaying, really. I think you're selling the kid short.