I've been vegan about 3 years. I'm in far better health now than then. My allergies have almost cleared up and I have lost weight. I work out in the gym and have not lost any strength. Other vegans I know appear to be dong pretty well as well. There are so many vegan options and alternatives, staying healthy shouldn't be a problem.

In regards to children, I have not looked into any research which compares children on vegan diets to children not on it. I will definitely put it on my list of things to do.