At a young age of three, I observe some of the children from public playground that they "know how to bully" other children their age. What to do when the guardian/parents doesn't mind the wrong doing even they see it. My concern is not about my child, coz he knows how to "stay away" from those kids. Will it be okay to approach and tell them what's seem to be obvious?

Actually I grew up at the playground when I was a kid - everyday 2 hrs rain or shine. I think it's inevitable that there is some ganging up etc. I will observe if they can manage it among themselves - because such things will happen many times throughout their lives and there won't be someone bigger/mightier to always help. If they can't then I will step in and show the naughty ones who is the boss. LOL - actually just introduce fairness and empathy and what should be the way. Kids are often in such situations