children pushing another

It has happened to my lo few times already he is being pushed by other children in playgroup. Lo never done anything wrong but wanting to play and associate with others. Sometimes he has been pushed and my first reaction is to get him away of it but i feel like im wanting to tell something to d child who did the pushing but i cant thinking that i might get conflict with d parent. But at d same time i feel for lo that he has experienced that and all i can do is hug him and take him away. He is a happy kid though he has not cried everytime it happened, he thinks its part of the play.