According to the Mayo Clinic the recommended dietary amounts of vitamin B12 vary. Experts recommend 2.4 micrograms a day if you are 14 or older, 2.6 micrograms if you are pregnant and 2.8 micrograms a day if you are breastfeeding.
The Mayo Clinic states that recommended dietary amounts of vitamin B12 are not available for those under 14. The adequate intake level is 0.4 micrograms for infants 0 to 6 months old, 0.5 micrograms for infants 7 to 12 months old, 0.9 micrograms for children 1 to 3 years old, 1.2 micrograms for children 4 to 8 and 1.8 micrograms for children 9 to 13. Doctors sometimes treat specific conditions, such as canker sores and anemia, with doses exceeding the recommended dietary amounts.