Vegetarian and vegan diets can be a healthy way of eating for all age groups - provided that enough thought is given to balance youngsters’ diets. There are potential pitfalls (getting adequate amounts of B12 and iron, for example, is likely to require planning) but provided that parents (and teenagers) understand how to balance their requirements, vegetarian and vegan diets can be healthy and adequately nutritious.
Source:http://www.bbc.co.uk/food/vegetarian_and_vegan/children.shtml#top