I could be wrong but it seems to me that there haven’t been any studies on the impact of being vegan all your life, from birth. I have been doing a bit of research into this lately (just internet research!) as my dd decided to stop eating meat (although she is not vegan) and I think part of her reason (as a young teen) was the fact that quite a few of her friends have become vegan.
It seems to me that you have to be incredibly disciplined to make sure you get all the right nutrients...