TrowelAndError - I don't know if he clambers or not I know I don't I bet the children don't even notice me taking the photos - I never ask them to 'pose' for a photo if it's not 'my' event.
Thinking about it, as I have, since I posted - I guess I take loads of photos, but most of the time at 'my' events or friends kids parties etc and I know how much they appreciate any I give them (many are on walls, in albums, photo frames etc). I guess most other parties are 'drop & run' so no photos! But I do take them when we meet up at soft play, the park etc.
It just gets up my jumper that people seem to jump to the conclusion that you are some kind of weirdo for taking photos of children.
I used to like taking photos at the local park as the trees and colours of the play ground equipment make for great photos - but I rarely do it now and seldom without kids in tow - but if I do, I ask the parents if they mind first. If I take photos of my kids and other kids are in the background then I don't ask though.
Of course someone can ask you to stop taking photos of their children and if asked I would - it wouldn't stop me thinking you were being precious (unless I was being really creepy and following your child around and only taking photos of him/her!!).
As for painting v photo - I know what you are saying, but it's the best comparison as to how I feel about my photos - that they are mine, my view and personal to me. I woudn't take, like 20, of you and just you, without asking - but you might be in the group, background of 20 photos... to me, there is a difference although I am not sure I'm explaining it very well!!!