Your use of "vegetarian" and "animal protein" are unconventional. "Vegetarian" generally refers to someone that does not eat meat but does eat eggs and dairy, so when you said "vegetarian kids need animal protein", it implies they need meat. But meat is not essential for development; B12 is, and can be got from milk or eggs.

It's true anyone raising their child vegan ought to be aware of B12 deficiency. Time was when B12 could be got from dirt on vegetables pulled from the ground, but nowadays we're pretty finicky about cleanliness.