Quoting The Fantastic 4:" In all honesty what privacy do children need in school except for rest room and locker room use where ... [snip!] ... clip about this little boy in day care beating up very young kids (toddler and a baby) behind the teachers back? Scary smurf "
It's just the law at this time. Does a class of kindergartner's really have anything that secretive going on? No but everyone may not agree to some stranger watching their kid. Could be a perv or something out there. I did see the video about the older kid beating up the younger ones, but I think that is negligence on the daycares part. They knew that kid had a problem to begin with and put him with those kids. And ignored when the younger children started crying.
But even with having video monitoring, like if it were in every class room or something the people that wanted to do those things would find ways around it. I'm sure the teachers that were caught doing those things weren't doing it in front of the entire class room.