Built -in-therapy is (God's blessing. I have one child with ASD and 3 (very close in age) who do not. I believe that having the siblings around him all the time has been therapy over the years. His older bro (by 18 months) is extremely smart, talented, and challenges him all the time. His younger sister (by 22 months) is only five and reading at 2nd grade level and has more friends than I do (social butterfly) also challenges him.

I have 5 year old twin boys. One of them is diagnosed with Autism when he was 3. Having a twin to challenge him has been built-in therapy...a real blessing. I'd be happy to talk to you more...you can also read my story on my page.

http://www.bellaonline.com/articles/art22966.asp
Google twins with ASD, there are a lot of articles that may help you understand better, Good Luck!

Yes, it's so amazing! By the time Seth was 3 he was reading at about a 1st grade level and this challenged Ethan (his non-ASD twin) to want to read (because of all the attention that Seth got from people when they realized he could read). They are now 5 and going into Kindergarten this coming fall. The therapists and teachers said Seth is now reading at about 4th-6th grade level, and Ethan is reading at about a 2nd-3rd grade level. I didn't push them to read in any traditional or formal way, either. And I have to confess, I didn't read to them that often, but they always had books around and loved them. I gave them educational toys (leap frog, etc) and only let them watch educational preschool shows (nick jr & disney jr). Now I'm afraid they're going to be bored in Kindergarten...Hopefully at this young age, they'll be excited they know what the teacher is talking about and not become behavior problems.