In kindergarten I used to be super helpful and nice to a little chinese boy in my class because I thought he was blind
What what this Chinese kid like?
He was nice. He had bowed legs and he always carried around an umbrella to protect him from the sun shining in his eyes Haha
You still had great intentions even if you were wrong, you were all just children. It's fine that you feel a little shamed from that, because it was an honest mistake. As long as you don't intentionally treat others differently it's okay.
But I thought he was blind. It makes me feel stupid now. Somehow I can't get over it.
You are fine, you helped him regardless of that. Its not shameful to be mistaken. You were young, and now you can just think about how you learned from that situation and were of service either way.