In this op-ed by Amy Lanou, Ph.D, she lays out the case that a vegan diet for a child is just as healthy and probably safer than the typical American diet:

Health by Veganism

In a side note, Clark Hoyt of the New York Times mentions the problem with an op-ed by Nina Planck called “Death by Veganism”. Ms. Planck claimed that a vegan lifestyle for a baby was irresponsible. She was wrong, of course. There is plenty of evidence to counter her claims. Hoyt’s point, concerning Planck, was that the Times didn’t present the other side of the debate, and has not presented the other side in sixteen years.