Situation with bratty older child at the park?

My husband and I take our 2 year old son and 3 1/2 year olds to the park just about every day and it never ceases to surprise me the lack of parenting done by so many people. We have had kids hit/push ours, take things from them, push them out of the way for the swings/slides, tell them they are not allowed to swing in the swing next to them. Even little kids like 4-6 will say horrible things to my kids. We live in a nice area too! And most parents don't see it because they are ot busy not watching their kids or don't care. I am not a helicopter parent by any means but I find myself having to follow my kids to make sure they are treated badly.. It's annoying.