Plot hole: When the aliens kidnap the adults, the kids are left behind. But all the kids seen are around 11 and younger. Where are the teenagers or young adults? None of them are during the celebration scene nor in the arena on the alien planet.
Plot hole: At the beginning of the movie, Jimmy's rocket could barely stay in one piece, much less leave the atmosphere. And that was only one rocket. But later on, not only can he build a much better rocket from one of the rides in the amusement park, but he can build ones for the other kids as well. It's not like he got better at building rockets, he tried to build another one in his yard before he and the town's kids did, but it fell apart.