Since autism has been shown to be associated with changes in the structure of the brain including in some cases a section of the brain stem that is missing entirely, it's not at all clear that providing vitamin D and feeding non-allergenic foods is going to solve the problem.
That said, I do have some friends with a daughter who had been diagnosed as autistic and who has no vocabulary at age six. They did discover that removing wheat from her diet caused a considerable improvement in her behavior. They ascribed this improvement to the fact that their daughter had previously been in pain when trying to digest what products. But their daughter still has extremely severe problems. She has subsequently been diagnosed with Angelman syndrome.
I had nad not heard about the missing brain stem. Obviously, different severities of the underlying conditions would be expected. I would have hoped that vitamin d could reverse some of the symptoms of young children. In many cases that would seem to not be possible. God help the parents of autistic children and those who believe autistic kids are brats. Thanks for your contribution.