I am not a vegetarian, but my family eats "veggie" about half the time. My son often prefers to not eat meat, although as a toddler (he is 2 1/2) we often measure his diet as "balanced" only if we look at a week's worth of foods...sometimes he likes mostly fruit, other times (like last night) he only likes veggies, and still other times only meat or protein (non-meat). We give him what we eat, when we eat it, and supplement with healthy snacks, as well as treats on special occasions (holiday goodies!).
Have you looked up naturopathic sources to get info on nutrition for your babe? One I use all the time, even tho I am not a vegetarian, is "Healthy Healing" by Linda Page, ND. It is revised every year or two, & has great info for both adults & kids. The author is vegetarian, & she also has a great website that might lead you to more info that could be helpful... www.healthyhealing.com
Another good baby food book I tried is "homemade baby food", it includes some meat recipies but has some great non-meat meals as well!
One thing my son loves is fresh juice, made in the vegetable juicer. We dilute it by 1/2 (& usually he likes it better when the weather is warmer, since juices are a cooling food), but juicing up apples & carrots as the base, & then adding just a *hint* of other veggies (like broccoli, beet, celery, spinach, that sort of thing--consult a juicing book for good recipies w/nutritional content) is a yummy & healthy treat.
Juices won't give him a complete protein, but thru beans & brown rice, other complete protein meals, a varied diet, &/or some of the other great veggie products out there these days (we love "Quorn", which is made of mycoprotein--mushrooms), you can easily give him the nutrition a growing boy needs.
You might check into bee pollen, as a yummy protein supplement, once your son is over the age of 1, & you know he isn't allergic to bees.
We also like a liquid kid's multi-vite that has green superfoods in it (by Natrol).
Hope this helps...