The sudden deceleration probably killed the entire crew.
The damage to the train, cargo and railroad probably will reach millions.
By the way the wood splinters are flying, the train is still in movement, so either the splinters turn the kid into ground beef or he gets hit anyway.
Vriska is a bitch and probably planned all this.

That was going to be the plot of the movie, but the director had to leave halfway to direct Breaking Bad, so the second half becomes that mess about the woman also having powers and yadda yadda.

Apparently there was going to be a part where he accidentally kills a kid while trying to save it.