Child who kills in self-defense--what happens?

What would happen if a child (pre-teen) killed in self-defense? I'd assume it would be considered manslaughter due to the self-defense, and the child will be tried as a juvenile, but what happens after that?

How long would the trial take usually? Do children in these cases just go back to their "normal" lives and return to the schools they were attending? But if the cases are public knowledge, how would other children, and other children's parents react to the return of the child? Would the child be shunned? Feared? Do most children in such cases end up moving away and attend a different school where no one knows him?

Whichever state the incident took place in isn't important to the story at all, so it's not a limiting factor (meaning I can have the story take place in any state that has laws matching my needs for the story. In fact, I even want it to be completely irrelevant where the story takes place, as technicalities are totally not the point of the story--it's a modern fair tale, but it has to happen in the real world since it's an urban fairy tale).

Whether the prosecution in the end would conclude the child is innocent is kind of tricky, as there are no witnesses. Essentially, this is what happens:

-Child A kills the adult while defending another Child B from abuse by an adult.

-When the authorities finally find the two children after months of search, Child B has disappeared, and Child A cannot explain why, because the disappearance was supernatural.

-Child B is the only witness to the incident.

-Child A cannot tell the truth about the supernatural disappearance, because of the consequences of being labeled as insane, so Child A lies and says they had a fight and went their separate ways, and Child B is still out there somewhere, living in the streets.

-It's common knowledge that the two children were very close--BFF and romantically involved.

-It's also common knowledge that Child B has become mentally unstable in the recent months leading up to the incident.

-I'm not sure if I want to have a witness to the supernatural incident where Child B just vanishes. It depends on how such a witness will impact the outcome of the case. I have no idea how supernatural incidents are perceived by the court of law.