I think it would be true to say that there are certain nutrients, notably some essential amino acids, that are not easy to obtain on a vegetarian diet. While this might not be too much of a problem for adults, it can be for children.
Which is to be expected when we try to exist on a vegetarian diet and ignore the fact that we evolved as an omnivorous species.
The trouble with that is twofold, Len.
The first is that omnivory is a fact and not an obligation - it tells us what
is the case (humans can digest flesh as well as plants) and not what
should be the case. In philosophical terms it's a fact and not a value, and you can't get the latter from the former.
Secondly, as I've very recently said, there have been happy and healthy thriving vegetarians and vegans by the millions for thousands of years, predominantly on the Indian subcontinent. Almost all of this vegetarian/veganism has been religiously inspired even amongst non-theists such as Buddhists, Jains and many Hindus, it's true, but the point is that if the nutritional illiteracy on display in this thread had been a feature of these people, say, two and half thousand years ago they'd have died out pretty sharpish. They didn't know, but we're now in a position to know, that well-planned and varied vegetarian diets protect against certain diseases and conditions - principally the big killers of overweight and obese people living sedentary, affluent lives: cardiovascular disease, diabetes and various types of cancer first and foremost - and may well even extend lifespan.