Cobalamin is added to any number of foods (usually in the form of cyanocobalamin), including bread, cereal, orange juice, soy milk, veggie burgers, soft drinks, and on and on. It is produced by bacteria.

I know multiple mothers who have breastfed while on vegan diets. It is trivial to get B-12, simply by taking a multivitamin, which they should do anyway regardless of diet (starting with prenatal preparation including folic acid supplementation).

I would suggest doing more research on the subject of veganism and discontinuation of spreading further misinformation.