Who cares what genre it is; it's a combination of all three, and while you've seen films with similar plot lines like this before, you know what to expect and even how it might turn out, but it's still worth the watch to get there.
This is a slow burn film, with no wasted scenes or padding, with believable and sympathetic actors, and you don't really have to suspend disbelief because the girl and the boy act like real kids would act around parents and adults. True, the girl is a bit smarter at the end than you may have thought she should be, but since it's only one small contrivance, it was acceptable as it was needed to get to a satisfying conclusion.
This is a slow burn film, with no wasted scenes or padding, with believable and sympathetic actors, and you don't really have to suspend disbelief because the girl and the boy act like real kids would act around parents and adults. True, the girl is a bit smarter at the end than you may have thought she should be, but since it's only one small contrivance, it was acceptable as it was needed to get to a satisfying conclusion.