How difficult is it to raise a baby on a vegan diet?

Supplements advised. It can be done, but there are certain essential nutrients that are difficult to obtain, so supplements help. The best food for infants is breast milk- not vegan but strongly advised. When done breastfeeding hemp or soy milk is a good protein source. Supplement with vit b12, taurine, carnitine & dha- these are hard to get from a vegan diet but are available from vegan sources, like dha from algae.
Don't do this. The long term effect of a low fat, vegan diet is malnutrition. Used for a short time (4-6 weeks) a low fat diet can be employed for weight loss. However, the long lerm effects of low fat diets are miserable. A low fat - high carb diet will lead to high Insulin levels, high triglcyerides, low hdl, metabolic syndrome and finally high blood pressure, diabetes and heart disease.