Recently I have noticed that my preschooler is staring at people with disabilities. I keep telling him that it's not polite to stare. The other day while we were on an elevator with a man who was using a wheelchair, my son asked, "Why don't that man's legs work?" I had no idea how to handle this situation without making it worse than it already was.
Your response to your child's question must provide specific information and help the child to see the whole person, not just his disability. Explain to your son that the man might have been in an accident or had a disease that left his legs "not working." Ask your son to think of things that this person might have to do differently than he does because of the disability. Bear in mind that some children are afraid of illnesses and think that if a person has had an illness or an accident it may in some way be contagious. If this is the case with your child, you might want to add information to allay this fear.
It is best not to silence your child without providing information during situations like this one, because that will imply that asking the question was somehow wrong. It might also be useful for you to take the lead if you see your child staring at someone, and ask him if has questions about the person that you might be able to answer. The key to answering questions at this stage of your child's life is making sure that he has the most exposure possible to diversity so that the questions will be asked naturally as part of everyday life.