I don't know much about how you are supposed to feel about these things, but it dosn't matter anyway. What matters is that you do have feelings about this thing and denying it won't change it, naither will feeling guilty about it.
I think your teacher was wrong to stop those girls from crying because if they need to react that way they should be allowed to do so.
Maybe you are feeling guilty and that is why you make things worse for yourself. Small children are very sensitive I have heard. Maybe Seeing and feeling the other children being hurt and just knowing something bad had happened, could have made you feel the same way. Maybe you were at a stage where you where learning about how to feel and react to different things and that could have made you vulnerable.
You can't meassure how much effect a happening is going o have on a person, it all depends on how you were raised, where in life you were, how others reacted, what mood you were in, everything.
For example some days it might make you mad when your little sister flicks your ears and other days you just think it's funny. We're all so very different, and being affected by this dosn't make you a bad person. I'm sure the people close to this were helped, you weren't. It makes a difference.