I have read many of Spero's posts in the past and find her to be a very lovely and knowledgeable person.
So my comments are not at all directed to her, but just general.
That said I wanted to make some comments, even though I have not managed to read all the comments! But wanted to have my two peneth worth, I hope that is OK. And I'm sorry if I say something someone else has said or not.
I do think it is wrong for places to make up rules based on 'not real' laws but I also think it is totally reasonable for individual places to say they will not allow photography either on their premises any time or at certain times (e.g. I believe there are rules about photography on the underground and also some churches will say you can photograph or record during worship services).
I totally agree people will want to take pictures of their own kids on stage and maybe a school should allow it if they are alone. Or maybe the kids who want to be photographed could be photographed at the end.
Maybe it is not against the law to take a photo of an unknown child but I cannot see any reason why anyone should be allowed to do it without asking the permission of the child, or adult with them, (just as I would not take photos of random adults).
The main reason this whole topic is a problem is because of social media and some people's desire to record almost every moment of their own lives (yes but of an exaggeration, but still!) and place these moment in the media. And that they may also in their zeal end up posting pictures of other people's children.
I think it is also important to recognise that the individual children's right to have their every moment recorded, or the parents right to record their children in many different situations should not be valued as greater than the right of children to live in peace and safety. This need of peace and safety and relative anonymity is when there are abusive parents/ex partners of parents/ or potentially risky adults or difficult situations that the child could be thrown into if their location is made known.
As far as the anonymity of the stage goes surely that is also dependant on whether or not the person posting the photo chooses to say 'This is St Elphin's school play in Lower Dungchester'!
Also there is (I believe) already some form of face recognition software, which means people can search photos on line. It might just be this that the vicar was thinking of.