Unless he’s up around 15 or older, I say, he’s just a kid. No guilt necessary. And unless his parents were criminally neglecting him in some way, same to them. We can’t start expecting kids to have adult capacity all of sudden. They simply don’t have it.
How many kids have played with matches? Most of us at one time or another I would assume. What happened is horrible, but an accident nonetheless.
As the saying goes:
There but by the grace of God go I.
It’s up to his parents to make sure he didn’t have the means to start a fire. His parents and their homeowners insurance company are going to be on the hook for all damages. No collage education for this kid and no retirement for his parents, unless they declare bankruptcy and start over from scratch.