Everyone more or less laughed and made fun of special children (and also "weird" or "abnormal" people) at one point in their lives, you'd be lying if you deny that.
My question is,
Why do we laugh?
Is it because it is genuinely funny, thus we laugh?
Is it to make ourselves better? if so what's the difference?
It is genuinely funny because they aren't normal.
Is there something wrong with that?
Well, you don't laugh when you are alone with the child, so it's not funny.
I think it's more of nervousness around your peers.
Try to understand them, everyones no rights or authority to laughed them but try to give them care and love and try to feel them that they are normal person that has no disabilities.