OK, I admit that the premise for this movie is rather horrifying, and in clumsier hands it could have have gone horribly wrong. And I'll admit that the overall plot arc and ending were pretty much exactly as one might have predicted.
But sometimes the journey is the reward, more than the destination; and even though we all know where the story is headed, just how it gets there is charming. And it's nice occasionally to see a movie where every person is basically nice and decent, which is funny but in a gentle way, which looks like some kids just having fun.