How would you react?

At playgroup my son (3yrs) and another little boy had a bit of a 'rift'. My son was sitting on the top of the slide, and had been for a few minutes (trying to get the courage to go down it i presume). The other little boy seemed to have enough of waiting and pushed my boy causing him to fall off through the side (instead of falling foward down the slide). Both myself and the other childs mother had seen this- i collected my son, (not too hurt, scrapped knee bumped head) and went to talk to this childs mother (who was just sitting there), asking if she saw this and if maybe she could get her son to apologise (i'm trying to teach my boy respect, morals etc? and didn't want him to think he could get away with the same thing without a reprucussions if you know what i mean). The mother said she saw nothing wrong and it was my sons fault for being a little "wuss" I think that was the term used. I walked away i can't tell her how to raise her child? how could i handle such situation better?