Is Methycobal 500 injections twice a week a safe dosage for a 4 year old with a language delay?

Depends on illness. Vitamin B12 is a vitamin, which means it is a chemical that the body needs. If a child has an illness that leads to B12 deficiency, that child can take B12 orally or via shots, depending on the doctor's advice. Injecting a child with B12 to try to affect the language delay, but who is not deficient in B12, is hopefully not the case here. We don't poke kids unless there is a very good reason.