"I think that the alienation you are talking about is impossible for a pre-schooler to inflict on another pre-schooler."
I think it's just tough for sensitive people in general. My mother has stories of alienation going back to her first memories. To sum up these memories: "They didn't understand me, they didn't listen to me, they weren't gentle with me, I felt sad and alone."
This is how she felt when she was sent to kindergarten by her parents. It is how she felt when her brother teased her. It is how she felt when her friends made a club and did not explicitely invite her (she found out later that everyone else assumed they were invited
and so it wasn't personal). She always kind of felt hurt. She still does, LOL. We literally have to say to her, "Mom, I am telling you X. That does not mean I'm upset at you. I just have to tell you because Y. I love you." Otherwise, drama.
I don't dare imagine what she must have been like at four on the playground.
Sensitive children can be targets for bullying. I understand that. Just because they are sensitive does not make any individual hurt they suffer less important. It is important for a parent to recognize the sensitivity of her child and help the child deal with it.
It is NOT the responsibility of that parent to make sure all the other parents are making sure their kids are tiptoeing around that child, literally or figuratively.
I disagree that "One kid in pain is one too many." Pain and hurt are part of life. Disappointment is a part of life. Learning to deal with that is also a part of life.
I can see that right now you have a precious little baby, not even one year. Of course she's much too young to be learning her knocks the hard way. She's all squishy and vulnerable and small. The only thing she needs is kisses on her big fat cheeks.
But no matter what you do, as she grows, she will get knocked around at some point. (Chubby cheeks likely having faded... ) It is just inevitable and it's not our job as parents to protect them from that. From the worst hurts, we can provide a buffer. But if she is rejected, we cannot ask others to accept her. You know?
And my point of view is not based on an optimistic view of children. I know they aren't nice. I want to slowly introduce my child to the vagaries of playground and peer-group antics slowly, so that she slowly but surely develops the skills she needs to take care of herself as she goes into school, high-school, college, and so on. And that means stepping back.