Was it Hillary Clinton who said "it takes a village to rasie a child"?
I have never thought twice of telling off other children if appropriate. Maybe I'm just lucky about where I live (or maybe it is becasue we have a very big back garden so didn't need to go to the swing park that often ) but I've never really had to to "strangers" - and my friends have simialr attitudes to upbringing, so we have mutually told off each others' children.
I know dh had occasionally had qualms - although that has not stopped him. He has also been heavily involved in ds' primary school (as he was the one working from home) so was the unusual "dad who is often in the primary school". Fortunately the school is sensible in its attitudes.
I've been on here often in the past saying that we are doing our children a great disservice in not giving them the freedom to learn to judge and indepedence - and along with that, danger - for themselves. Ds has just started P5 and is 8 and has been walking to and from school on his own for nearly 2 years (only occasionally the first year and often followed by one or other of us) and really enjoys - and respects - the trust that we place in him. It's a 10-15 minute walk, with one lollilop man, but a couple of other quieter roads that he needs to cross on his own.
We have even, this summer, started to let him go the local park (5-10 minutes walk away) on their own to play football. Again, fortuantely, his friends' parents have simialr attitudes to the lack of likelihood of them being abducted/abused.
On holiday in Greece, we have let him to the local football pitch - a good 15 minute walk away, on his own.
We have taught him abut "stranger danger" - but in a very low key way and more in terms of not getting into strangers' cars and (more relevantly) if anyone (friend or family) wants him to do something he does not like and wants him to keep it secret, he should tell us. We have not taught him that the default position is to distrust all adults.
I think the more of us that "admit" to giving our children freedom, the better for society.