If, for dietary or ethical reasons, you have decided
that you want to put your infant on a vegetarian diet,
you should be very careful in choosing formulas and solid
food for your child.

If you plan to breastfeed the infant and you
are also a vegetarian, you may need to supplement
breastmilk with additional sources of nutrition, depending
on your dietary restrictions. If you are a vegan, or an
ovo-vegetarian, you should add sources of vitamin B-12 to
your child's diet.

Other than the B-12 supplements, your infant should be
able to receive all micro and macronutrients through
breastfeeding, even if you are on a strictly vegan
diet.

If you plan to use formula rather than breastmilk, you
should stick to commercial formulas, which contain the
proper amounts and ratios of nutrients. If you opt for
a homemade formula or soymilk over a commercial product,
your child could experience developmental problems from
a lack of proper nutrition.

If you want to keep your infant on a vegan diet, you can
select a soy commercial formula, as long as it is
nutritionally-adequate.

After about a year, you can begin to supplement formula
or breastmilk with other sources of nutrition, such as
homemade formulas, soymilk, yogurt, and cow's milk (if you
are not a vegan).

Nutritionists suggest that you keep your infant on a
full-fat, high protein diet after age one, which includes
vegetarian-friendly foods, such as mashed and pureed
avocados, soy milk, nutrient-fortified tofu, and yogurt.

When you are ready to switch your infant to solid
vegetarian foods, you can introduce solid tofu, pieces of
vegetarian burgers, eggs, and cheese.

If you supplement what a nonvegetarian diet lacks, maintain
a full-fat diet, and increase your infant's sources of
protein, you should have no problem maintaining a healthful
vegetarian diet during your child's crucial developmental
stages.

Vegetarian diets, alternatively, cannot simply provide babies all of the nutrition they require and thus these diets are not suitable for young babies, however, if you're certain this is exactly what you would like for your baby you must make contact with a dietitian first.

For nursing mothers i dont see any reason they should be a vegetarian because it is inhuman to the infant and also the mother can never supplement all the food components which breast milk of non-vegetarian nursing mother can supply to the child.
I advice nursing mothers as a expert in the field to: increase water consumption, eat more protein, eat a low fat diary product and friuit, eat food containing folic acid(vit B9), consume 1200mg of calcium and stay away from tobacco     

Nutritionists suggest that you remain your toddler on a full-hefty, towering protein eating routine following experience one, which includes vegan-accommodating sustenance's, for example pounded and pureed avocados, soy drain, nutrient-strengthened tofu, and yogurt.