First of all, don't worry: he's okay.
Little R was wandering around the in the waiting room as Little S was sitting on a chair and I was talking to one of Remy's therapists at his nursery school when suddenly another little boy started slapping and walloping Little R in the head. All of us in the waiting room were too shocked to actually know now many blows the aggressor manage to take on Little R before his foster parent restrained him. Quickly, one of the CDAs took Remy who was rubbing his head in just as much shock as all of us, to make sure he was nut hurt.
I can't tell you how ugly of a feeling it was to seeing my own child being physically attacked by another child. At the same time, my heart went out to the aggressor and especially to the foster mother. As soon as she restrained him from hitting Little R, he turned around and starting hitting, kicking and biting her. I could only imagine the anguish bubbling inside the poor woman.
I do read up on parenting and discipline techniques, but I really didn't know the proper thing to do in this case; I was too shocked. I just held Little R, rubbed his head, told him it wasn't his fault and that he should never hitting any like how the boy hit him. The other boy just kept looking around, the expression on his nondescriptive of what he probably felt inside: frustration? anger? He did not have the facial expressions or body language that signalled any aggressive moves on his part. What I have read (I remembered it only today) an adult should do when child A hurts child B, the emphasis to be put on child B (the victim) to make sure they are all right in front of child A. Child A must be ignored (well, actually we want to ignore the aggression action to deter it) so that he knows not to gain attention by being aggressive.
Now that the school knows about the boy's sudden aggressive tendencies, they will be more vigilant when he is in the classroom or around the other children. It was a good thing Little R was a tough and sturdy boy so he was able to take it.
I hope that the boy will be able to learn to communicate without violence and manage to communicate more effectively. As for Little R, we must teach him to put up his hands palms facing offender and shout "no!" He must learn to protect himself.