I'm sure there was a post on here weeks ago recommending 'my brother is different' for siblings of Autistic boys [theres also my sister is different for obvious reasons!] We bought it for our 5 year old, and he's really taken with it, and keeps reading it and announcing "thats just like elijah isn't it"
I'm really pleased as well, becuase it does explain autism in a suitable way for young children and I have really struggled to explain it in basic terms, espcially as ds2s autism becomes more nad more obvious as he gets older...