K.,
I just replied to your other request too. My son is 5, autism, and very self-limiting with foods. At this point he eats fewer than 12 different foods and things he will eat are brand specific (he will eat Velveta Shells and Cheese but no other kind of mac n cheese, etc...) You need an Occupational Therapist who specializes in sensory issues in young children who has a background in feeding issues. If they have experience with autism, that would be helpful too. There are different types of OTs so make sure you ask about their specialties. Where are you? I'm in Las Vegas, Nv. If you live here too, I can direct you to all kinds of resources.
We are doing Occupational Therapy and our therapist has been working with my son for about 6 months. She established a good relationship with him, worked on sensory issues first and she's recently started on the eating stuff (she said eating stuff requires a lot of trust so the therapist needs a good relationship with the child to be successful). I'm optimistic that we will hit upon something that helps. My son is on what she calls the "bland and white" diet. He'll eat mac n cheese, chicken nuggets, fries, french toast, apples, grapes, wheat thins, water, milk and pepsi (and of course he'll eat cookies, candy, donuts, ice cream and cake but I tend to not let him have those things - we seriously limit artificial colors, flavors and preservatives because he's very hyperactive and those things make it worse). And that is pretty much it as far as food choices. In my experience, the food limiting thing tends to get worse, not better. If I would have known 3 years ago what I know now, I would have started OT many years ago.
Keep in mind that you'll be getting tons of advice on all sorts of diets, therapies, etc... It is really important to do your research and then try things you are comfortable with and work your way down the list. You can't do everything, nothing works for every child, and so on..... Don't beat yourself up for what you don't (or didn't know) just move on if you try something and it doesn't work. All you can do is the best you can do with the info you have. You can drive yourself nuts researching and trying different stuff. One day at a time... One therapy or diet at a time... One protocol at a time...
The things that are PROVEN to work are therapies: ABA, floortime, Speech Therapy, Occupational Therapy, etc... So start there and then branch out into other areas.
T.