Since my daughter has grown up with others with special needs, this is an issue that has really not been an issue. I think that by allowing a typical child to ask questions about a special needs individual is a great way to break the ice. Children are honest if nothing else and even although their questions may be brutally honest, they need to understand, at their level, an answer.
For example, when a typical child sees another child who is in a wheel chair, explain the possibilities as to why that child is in the wheelchair. My daughter is ambulatory but has seizures and is developmentally delayed. She is 20 years old but still loves to play. She is great with kids because developmentally she still is a kid.
We've had issues with other kids with whom she wants to play "outgrowing" her and moving on to what others their age do. She doesn't understand, but we muddle through. She does have a friend we met when the friend was 5 and my daughter has 15 and this little girl is the most patient and wonderful kid ever. I like to believe it's due to the exposure she's had to my daughter and watching us interact.
As for teaching other typical kids, it's a matter of exposure and being as honest as possible in a language they understand. Having them help an individual with special needs, volunteering at school or church, camps, and even visiting a hospital are great ways to help them understand that even though we are all different, we all have the same need to be accepted for who we are as individuals.