Obviously you are upset, it's awful to see your child being pushed or hit.
I would like to gently point out that it can be hard to correctly age a child.
My niece, when little, and her young son now seem so much older than their actual age. They are both tall and big boned, always wore/wear clothes for at least two or three years older.
Many people, quite obviously, judge behaviour on what they see before them. It's not easy when a 2 year old is expected to have the skills and awareness of a 4 year old.
My approach would have been to say to the other child,
'Oh No, look, poor Fred has fallen over because you pushed him, he's very sad. We must have gentle hands when your play with other children, mustn't we? You are such a big boy you can show Fred what to do! Perhaps you could go on the roundabout, climbing frame, kick the ball?
I would then wonder over to Fred's mum
And say, 'oh don't worry, My little one was upset as your little boy pushed him, he's fine though, I don't want you to worry, he's going to show Fred how to climb, kick his ball.
Usually worked for me as a childminder.