I am not a child psychiatrist, but I was asked lately about MB12. As it was my first time to hear about the use of methyl B12 I went on reading a bit about it.
However, it would be more informative to hear your experiences with it, if you have any.
You can check this out but be careful in interpreting results: http://www.ncbi.nlm.nih.gov/pubmed/20804367. ASD is not a disorder with a single cause so until etiologies are better understood, take "medical" treatment studies with several grains of salt. Earlier studies of B6 and Mg efficacy didn't pan out.