Parenting <is> interesting territory, isn't it. Far more interesting even than marriage.
The Autism one - I was supposedly ADD (back then, they only had the term 'hyperactive" to use) and as an adult there have been lots of other theories about 'me' that are now either untestable or irrelevant since I'm all growed up. My personal preference would be to let a child know about their special difference from other kids at an age where they can process and accept it without labeling themselves, or worse, develop a crutch (I can't do this because I'm _____________). Because personalities are different, some kids are going to say the opposite, (I WILL do this in spite of my _____________).
I'm a pretty screwed up human. If I came from a factory, I would have been recalled. The ADD, hypersecreting adrenalin, a moderately severe scoliosis, hips cocked, legs different lengths - born 9 weeks premature in 1967, when they couldn't do a damn thing but watch to see if you lived or not - (and then, finding out I'm adopted, the fairly severe and frequent dad-beatings, etc) I mean, lifes tough and we all face our own barriers. I personally think that the decision to tell/explain these things is predicated on how ready the child is to accept it and how they will react, and how it will affect the way they approach everything that life throws at them. They should know. The question, really, is when. And you as parents will make the best decision you can, and it might work out fabulously and it might not, but you know, there is no instruction book, no oracle to consult, and every case is different, so it will be OK no matter what. Because he loves you and you love him and he trusts that you are trying to do the right thing all the time, and eventually, also understands that you don't always.
All the people on the board here who post about their kids and families are, as far as I know, terrific parents doing a really hard job that costs money and time, and they do it out of love for their children and spouse, and love for the whole idea that life, their life, goes on through their children. You are all awesome.