MedivinalGin and all thanks, it was creepy and I am not and by no means was not hysterical. It is a violation absolutely, particularly depending on the situation. And this is not a situation where my DS pics are in newspapers or the school website, all fine obviously.
Also, I've dated a professional & occasional street photographer and taken many photos out and about myself. This was not that though you only have to read debates around that kind of work and people like Diane Arbus, to see even there there are questions about were these photos violations/exploitations or not.
Also, this was not a group shot. He was directly across from us.
Anyway, this ended up being more than I wanted to say on the subject and actually I don't know what he did. I hadn't really taken my thinking so far as to what this might be for but it has been a good reminder about talking to my DS about staying safe in public now and as he gets older.
Personally, I wouldn't take a picture of a child without permission. Also, I posted a photo of myself pregnant with my belly showing on Facebook and it ended up on some random other sites, including a Chinese language one 😳
So, the poster that mentioned their child's photo everywhere I'm so sorry! That sucks. And also want to thank the poster who posted the transport police number. Going in my phone that. 
Anyway, thanks for all replies, good to hear a range of thoughts.