I also don't understand the very individualistic approach to parenting. I don't have children so I'm not speaking from a position of expertise at all but it seems that in the UK, you absolutely shouldn't concern yourself with anyone else's children or parenting at all (unless there is suspected abuse).
I find that so weird. Where I grew up, children really were raised by a community. You were just as likely to get bollocked by your neighbour, the shopkeeper, some random person on the bus as you were by your own parents. Parents didn't take it personally that someone else would tell their child off - the attitude was (is) if a child's being a twat, they need to be told enough and it doesn't really matter who does that.