Your work in "the field" must not be too involved, otherwise, you would know that the leading authority on nutrition, the American Dietetic Association, agrees that a vegan diet is completely healthy for any stage of the life cycle, including infants and children. You would also be aware that the idea of protein combining is very outdated. Though you are correct in the fact that individual plant foods are not complete proteins in themselves, it is very easy to obtain all essential amino acids by consuming a variety of foods. You do not have to eat beans and rice in the same meal (or even the same day) to get these benefits, as was once thought.