Telling Your Child He Has Autism

I chose to tell him while we were out walking. The three of them ran on ahead as usual, but I called Zeno back, put my arm around his shoulders.
"You know how Zudie is a little behind in some things?" (Zeno had noticed this and pointed it out to me). "You know, at his age you had me reading encyclopaedias to you and you loved telling people about how the solar system works. You were a little ahead of other 4 year olds. But Zudie isn't like that, he's a little behind other 4 year olds. "
"Yes, he doesn't talk properly at all."
"Well, it might be because of something called autism. The doctor we went to see thinks Zoudie might have autism. It doesn't mean there's something wrong with him, just something a bit different - autistic children are a bit different from children who don't have autism."
(I'm thinking, did I say that right? I wish I had rehearsed it a bit. And now that I've brought up the subject by referring to Zudie, it's time to carefully bring it around to Zeno).
"Sometimes children who have autism are a bit behind other children in things like speaking and understanding. Sometimes children who have autism are a bit ahead in some things."
"Have I got autism?"
The directness of his question knocks me for six. I had got all psyched up to tell him he had autism, and now that all I had to say was one word "yes", I was hesitating.
"Yes, you and Zoudie probably both have autism, but different kinds".
"Can I go now? I want to go in the phone box at the bottom of the hill."
"Ok, but don't phone anyone."
And off he ran down the hill after his brothers.
I know that right now he probably has no clue about what autism is, and when he finds out there might be trouble. There will need to be further discussions and explanations. But it's a good start alhamdulillah.