Mod Sam answered this on her personal blog and I loved her answer so I’m going to add it here and then add my own thoughts at the end:

Oh my gosh what a question. Where even to start? Okay. This is gonna ramble a little. There’s also going to be a little bit of stuff about halfway through this that might seem like scare mongering. There’s a point, and that point is no one ever tells us that. Give it a moment, it will make sense.

In my opinion the biggest mistakes that a parent can make with regards to an autistic child are, in no particular order:

Not telling themNot telling them before they start schoolNot teaching them to be realistic about their limitationsNot teaching them to try and reach beyond their limitationsNot teaching them the last two things are not contradictoryNot teaching them to stimNot teaching them ASLNot teaching them to ask for helpNot teaching them to set boundariesNot teaching them body autonomyNot teaching them consentNot teaching them to demand consentNot teaching them why it is not their fault when they don’t fit inNot teaching them why anything (seriously, especially for autistics)Not teaching them how to scriptNot teaching them scripts for dealing with authority during meltdown

Gosh, this list seems so short. There has to be more.

Look, the secret to parenting, from my perspective as a person who has been there done that as a co-parent a few times, is that you are going to do the wrong thing. Like, that’s just the reality of parenting. You’re going to fuck up. What matters is what you do when that happens, and what you do minimize the damage before it happens again.

Is 5 to young? I don’t think so. There’s age appropriate representation. Not a lot of it, but it is there. There’s autistic parents and autistic parents of autistic children to talk to. Ask their advice.

You don’t have to make it a big deal in the sense that it has to be a production, but it is a big deal. The scary truth is that autistics are exceptionally vulnerable. We have a very high morbidity rate from suicide and cops in particular. We have exceptionally high rates of unemployment even when we are otherwise able bodies. We have exceptionally low high school and college graduation rates. Life is hard for us, and we have to navigate all of this in society that also happens to give us high rates of cPTSD.

That’s the reality of our life, so yeah, it’s a big deal.

And no one ever tells us that.

Thing is, telling us that… stuff… that’s how you make all that stuff something we can deal with.

Over, and over, and over, the thing I hear most often from teens and adults who either weren’t told or got a diagnosis late in life is, “I wish I had known sooner.”

The easiest way to avoid the bad shit is to confront it. That’s what will give her the best chance. The hard part about all that, is figuring out what is age appropriate. Hardest part about raising a child that has a developmental disorder is that the whole point is “age appropriate” is different for each of us.

That’s where family is so important. We rely so, so, much on family to figure that one out for us. And yes, you’ll mess that up too, sometimes. My advice there, presume competence, don’t be afraid to ask her what does she want to know about whatever topic you’re talking about.

Get her the support she needs now, before she needs it. IEP? Get it. Accommodations? Get them. Teach her about the tools available to her - OT, CBT, therapy, medication, and teach her from an early age to take an active role in learning about these things so that when she needs them she is equipped to come to you with her needs knowing that she has options to help her. And when she does, help her make the the choice she thinks is right for her about what support she needs.

By the time it becomes a problem and she needs to know, it’s already too late. That, above all else, is why you tell her.

To add to what Sam said, I, personally, don’t think that it is ever to early to tell a child about their diagnosis. I think that as soon as it is known that a child is autistic, the child should know as well. Even if they’re only two or three, start using the word around them and getting them familiar with what autism is. 

As they age, you can tell them more and more. Like Sam said, open it up to whatever questions the child has. Allow them to inquire about their diagnosis and learn as much as they want to about it. 

As someone who wasn’t diagnosed until adulthood, I wish I had known so much sooner. I knew from the time I started school that I was different. I was bullied and mocked for my differences. Having answers for why I was different could have made all the difference for me. Instead, I have a blank spot in my memory where my childhood should be because of all the bullying I endured. 

I hope this helps!