if a child was in any danger or hurt or upset then i would act first and think later.
I would hope that any decent adult would do the same if my child were in trouble.
When on holiday a couple of years ago we were at a holiday park and the amount of lost children (my friend found a Downs child sat in her car one evening) was astounding. We took a few home to their parents, who were just enjoying their holidays, oblivious to what their children were up to.
One child was obviously lost in the entertainment centre, my friend and i walked slowly near her, never taking our eyes off her whilst our fellas found the nearest security guard for assistance. The mother, once found, didnt even say a word to us.
My son got seperated from me and Mr CRX last year at centre parks, i had left him with Mr CRX and walked away and little CRX ran after me. Mr CRX thought he was fine as i was so close. We didnt realise he was missing for 20 minutes and i have never been so grateful for a strangers help as i was that day. A lovely lady found him crying and took him straight to the staff, she even stayed with him to make sure he was OK til we got there.
Maybe i am too trusting but i feel that children do need to know that they can trust some people. Yes, tell them about stranger danger, but dont scare them into thinking that every stranger is a danger to them, they are not.