It seems to me that the problem stems from a different direction, as far as I know, B-12 is just one of the B vitamins, in order for the body to really absorb and benefit from ANY of the B vitamins we have to supply him with the entire B family therefore when you give your child shots that have just the B-12 you may see very little improvement if any.....
my son is 6 yr old severely Autistic, he was completely non-verbal, 3 month ago I started giving him B-complex from Shaklee, I give him 2-4 tablets a day, I crush into some grape juice and give It to him with a dropper (like Tylenol) since than he started having words! now he can name all of his foods and some of his toys and is asking verbally to take a bath! he is much more calm, less crying, more awareness and more facial expression!
when choosing supplements It is very important to have a company that is reliable has a commitment to purity and quality, vitamins are not drugs! you have to do your research about the company before buying them.
here you have a link were you can check out the Shaklee company, I am using their supplements for the last 2 yrs for myself with amazing results, and now for the last 3 months for my son with great results as well!http://www.raizy.myshaklee.com