1. These little people have to wrap their brains around issues that adults struggle with. Be honest and forthright as soon as they are old enough to understand. That time will vary and you and only you can make that decision. This is one the books, websites, and medical journals cannot answer.
2. Allow them to be as involved as they want to be. Grace, enjoys attending Kate's sessions (probably because they are play-based) but at some point I fully expect her to ask for a break and she will be welcome to it.
3. Make sure you dedicate special times where the focus is entirely on them. I am taking Grace away for a long weekend soon and it will be a much-deserved Gracie-centered weekend.
4. Allow them to complain about their sibling. In some sense, they may feel ripped off (back off haters, a four year old child does not have to see autism as a gift) and they may need to express how bad it feels. Some children may not want to say it to mom or dad because they can sense you have enough on your plate so please give them a cool 'aunt' or a grandma that they can complain too.
Have any advice to share?