I personally have several conflicting views on this...
When my DS was at nursery, a couple of parents didn't want their DC photographed under any circumstances. That was all well and good - and I totally understood the parents' point of view. However the nursery took it to an extreme and banned ALL photography (and cameras!) during events such as sports day. This was even if the not-to-be photographed children were nowhere near the potential photographer.
It's meant that I have no photo record of my DS when he was at nursery. It made a lot of parents quite angry at the nursery because they were too rigid.
Conversely, a close family member has just set up a holiday activity for children. We have spent a great deal of time thinking up a policy for our "official photographs". So, we are very aware that some parents don't want their DC photographed and have an official policy.
However, this doesn't stop other people photographing/videoing children when their child is participating in this event.
On another track... Many many years ago, before FB and social media, DD was (unknown to us) photographed by the official photographer at a very large international event. The next year, her photograph was used all over their advertising - bill posters, magazine articles, flyers, leaflets - you name it, her face was on it! We only discovered they'd done it when we went to the same event the following year. (She'd changed so much in that year, that I honestly didn't recognise my own daughter, until she pointed it out that it was her!
)
I was very
about it as it was without my consent. So I approached the company - who told me to go away because just by being there it was a public event and they could do what they wanted with their photographs of my DD. I was even more
at that response! But because they sent me a whole host of literature with DD's face plastered all over, I decided not to persue it. It's now my DD's 15 min of fame 
Still not happy it happened though but I don't think you can stop people filming/photographing their children and your child gets "caught" in the camera.