SSI for autism
One of the recommendations for parents raising an autistic child is to apply for disability. You may or may not be approved, but even if you are denied it's not the end of the world.
Two things about a denial. Expect it and decide if you want to reapply. You don't have to, in fact many people only apply for the denial which can help with the process of applying for Medicaid. Medicaid often wants to see a denial that way they know your child doesn't qualify for Medicare.
It;s a weird system how it all works, but if you can't qualify for Medicaid based on your salary this is usually the route to go. I recommend asking for advice from a social worker with medicaid as well.