Can Someone Help Me Name That Movie?

I watched this movie when I was younger. I don't remember the name of
it, just random scenes from it. Can someone help me figure out what
movie it was?
I believe the movie was about this smallish group of kids going around
town trying to destroy this ghost that took form as a child.
One scene I remember was either one of the girls or boys was in the
subway area and the little ghost boy was pretending to get his foot
stuck in the tracks so that when the other kid came over to help him,
that kid would get stuck and get hit by the train.
Another scene I remember was all the kids putting their hands on this
crystal ball-like thing attached to the top of this short post at an
amusement park or some place like that and that started to destroy the
little ghost boy. It showed the little boy aging until he basically
vanished.
Any clue to what this movie could be?