This vitamin is essential for the growth and stability of neurons. It’s actually involved in the production of nerve cells and for making the myelin sheath that protects our nerves. Short term deficiency in B-12 can show up as fatigue and lethargy but a long-term deficiency can result in damage to the brain and central nervous system. Stores of B-12 can be low in children not getting any dairy, cheese, or eggs in their diet. Very commonly we see low B-12 levels in kids with Autism Spectrum, sensory, and behavioral disorders. The recommended daily amount of B-12 ranges widely based on the person and severity of the deficiency (100-1000mcgs). This is a vitamin that you will want to get tested and have a nutritionist recommend a safe daily amount for you or your child.
B-12 is strictly found in meats so there are no vegetable sources of this vitamin naturally. Anyone who doesn’t eat meat on a regular basis would need to supplement. It is found in all “flesh foods”.
•    Beef
•    Chicken
•    Salmon
•    Shellfish (especially clams & crabs)
•    Tuna
•    Turkey
•    Veal

I would recommend starting with beef, chicken, and turkey and slowly start adding in other forms of meat into your menu. Swapping white fish for chicken or turkey along the way is an easy way to introduce new foods into your family’s rotation. 

*Again, the majority of this information comes right from “The Disconnected Kids Nutrition Plan” by Dr. Robert Melillo. I highly recommend this book for the exact science of the elimination diet and ways to help your family’s overall health!