I imagine it is strictly related to the changes in the body and not the moral aspects that go along with those changes since they are just fifth graders.
I wouldn't assume anything. In a public school, you never know. Maybe you can go to the school and preview the video without having to take it home. I would also ask the teachers exactly what will be said, if anything, before or after the video. Will there be time for Q&A by the kids? If a kid brings up a "controversial" topic such as homosexuality or birth control, will the teacher answer in front of the class?
I know it's a difficult situation because on the one hand, you want to make sure your child isn't taught secular non-sense, but on the other, how would he feel if he is the only one in the class whose parents didn't allow him to participate?
I would think previewing it at the school would be a possibility. You had better hurry up with going to do that.