The Academy of Nutrition and Dietetics and American Academy of Pediatrics agree: Well-planned vegetarian and vegan eating patterns are healthy for infants and toddlers.
Time and attention are necessary to help young children, vegetarian or not, get all the nutrients they need for normal growth and development.
For the first six months, all babies do best with breast milk. Use iron-fortified formula (soy for vegans) if breast-feeding is decreased or stopped. Cow's milk, soy milk, rice milk and homemade formulas are not appropriate for babies during the first year because they have the wrong ratio of protein, fat and carbohydrate. They also are missing important nutrients for health, growth and development.
Solid foods can be introduced in the same way as for non-vegetarian infants. Replace meat with mashed or pureed tofu or beans and soy or dairy yogurt and cheese.
Since breast milk is such a rich source of nutrients, vegan mothers may want to breast-feed for more than one year. After 12 months, vegan infants may be weaned with soy milk fortified with calcium and vitamins B12 and D. If a vegan baby is weaned from breast milk before 12 months, they should receive vegan infant formula until they are 1 year old. Milk alternatives, such as soy, rice, almond, hemp, etc., are not recommended during the first year of life as a primary drink because they do not have the right amounts of nutrients.
Nutrients Needing Special Attention
When feeding vegetarian or vegan children, pay close attention to the following nutrients:
Vitamin B12: Vegetarians can get plenty of B12 from milk products and eggs. Vegans, both breast-feeding moms and children, need a good source of B12. Options include a supplement or fortified foods such as soy beverages, cereals and meat substitutes.
Vitamin D: The AAP recommends all breast-fed infants receive 400 IU per day of supplemental vitamin D starting shortly after birth. This should continue until your child consumes the same amount of vitamin D from fortified milk: at least one quart per day of cow's or soy milk.
Calcium: Breast- and formula-fed babies, as well as toddlers who consume milk and dairy foods, usually get plenty of additional calcium from foods including yogurt and cheese. For vegan toddlers, calcium-fortified foods and beverages or supplements may be necessary. See a registered dietitian nutritionist for advice.
Iron: The iron content of breast milk is low, even if moms are eating well. Babies are born with enough iron for 4 to 6 months. After this age, vegetarian and vegan infants need an outside source. Options include iron-fortified cereals or supplements.
Protein: Babies need plenty of protein for rapid growth during the first year. Protein needs can be met with breast milk or formula until about 8 months. After that, add plant proteins from beans and cereals, and fortified soy milk after 12 months. Lacto-ovo toddlers can get protein from yogurt and eggs.
Source: https://www.eatright.org/food/nutrition/vegetarian-and-special-diets/feeding-vegetarian-and-vegan-infants-and-toddlers