Nik's Mom, if you don't make a big deal of of it, then they won't either. Just start mentioning it from time to time in conversation. Things like "I think it's great that you think that way, it's one of the pulses to being ASD" things like that. If you mention it casually, but always with a positive spin, then they won't get the idea that there is something "wrong" with them. This also opens the door for them to aks questions when they are ready to. Don't forget, that it might be a big deal to us, but not a big deal at all to them. When I told my oldest after a big build up, he just looked at me and said "well, duh!"
I also used to use phrases like "boy it must be so boring to have regular kids!" Or my favorite, and the one I use most often when the boys are really having bad days - "Fun with Autism!" This kind of phrasing lets the boys see that they are unique, but also that I wouldn't trade them for anyone else. Good luck!