Different parishes offer different services to parishioners.
This article was in Michigan Catholic and talks a bit about SPRED, which is the Catholic ministry geared towards special needs religious ed. Try to find a parish which is open to it.
I also found out about a special needs program at a local parish through Twitter by"following" the Archdiocese of Detroit.
My son isn’t autistic and is in mainstream Kindergarten. He has a speech delay.
I wish I could give you more information. One of my girlfriends has two severely autistic children, but doesn’t take them to mass because of the severity of their autism. I’m not sure if she’s going to try religious ed when they get older. (They are already 6 and 3.5)
Good luck to you. I hope that you find the parish and resources you need to teach your children the faith. Hopefully, someone from TX/Corpus will be able to answer your question better than I did.