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?

For me I will tell the kids off. There was once I brought my then 6 mth old to an indoor playground n there were 2 boys ard 6-7 yrs old trying to bully my LO n didn't allow him to play n tried chasing him away even when I'm with him! When I told them sternly that that is a public place n shared playing they still dare to buzz ard me to chase me away! Until I have to ask them where their parents were