My son is 4.5 and has a new boy starting in his pre-school class who has cerebral palsy. The new boy's mom is nervous that her son will struggle not knowing anyone and with others not being kind to him because of his condition, so we have arranged for a playdate before he starts so there will be a familiar face at pre-school etc. I know from speaking to her previously that she can be sensitive to people using insensitive language to talk about her son's condition and experience and has been offended by this in the past.
I was just after some advice from moms with experience of what would be a sensitive way to explain questions my son might ask of why the new boy is different from him. He will be at mainstream school when he goes, so his abilities aren't that different from his peers, but his mobility and speech are notably different from my son's at present. I guess I want to avoid being put on the spot by my son asking an awkward question while the new boy and his mom are with us and answering with a term that could be taken as insensitive. I would naturally feel inclined to avoid negative terms like "there's something wrong with..." or "xxx doesn't work properly", but equally feel that just using "differently" ie, "his legs work differently from yours" might get a bit clumsy and might just encourage another "why?"
I don't forsee this being a major problem; hopefully they will get on fine and my son won't have too many questions, but I just want to be prepared and don't want to offend inadvertently.
My dd is 3.5 and has CP. It is mild and she comes off as being clumsy and inarticulate. No one has ever brought it up at her school. (mainstream preschool) other than teachers. The kids have never said anything at all. They just play together nicely. Granted your chid is a year older- so might call out differences. I think I would go the route of not mentioning it at all and letting the kids get to know each other. If your DS asks questions the other boy or his mom can help answer the questions how they want to.
In a Kindergarten classroom I was in this year, there was a little girl whose hands and arms hadn't formed properly. The teacher was all geared up for the other kids to ask questions, but they never did. They just accepted her at face value and helped her out with things she needed a hand with.
CP is a pretty big range, and depending on this little boy's specific abilities, your son may have questions. One of the kids at our school has CP and is in a wheel chair and has leg braces. Kids have asked me why, and I've told them that is what works best for him -- just like some kids wear glasses to help their eyes. The conversation quickly went back to something else.
I think some of these things are actually a bigger deal to ADULTS than they are to kids, or perhaps children have an intuitive understanding that going on and on in front of another child and school personally isn't OK, even if they would badger their own parent senseless trying to make sense of it.
As far as your son, you can remind him that everybody is different, and that every body has things that are easier for them and things that are more difficult for them. The ability to be kind to others and to share, are some things that I'm sure he has seen other kids really struggle with.
My advice is to find out a bit about the boy and plan activities for the two boys that they can both really enjoy and immerse themselves in, because once they get busy having fun, the differences will be in the past. What kids really care about is if they can PLAY with another child.