joe, pragmatically, can I point out two things which you may not want to hear but which are true. If you take your son out of this he is going to be, I expect, one of only a few children, maybe even the only one. This is is likely to single him out in the class which can be hard for a 7 year old, especially if its hard for him to understand why, The second point is that all the other kids will have seen the vid and will be discussing it....even if you take him out of the viewing, he is going to get the information only probably horribly garbled as kids do.
Do you want either of those things?