Just tp add some reasurrance. my DD (2.5) is veggie and does not have any supplements, just a very good diet. I find she'll eat fruit and veg till the coes come home. A good and simple meal is lentil stew. Just make the lentils (takes about 20 mins to cook) and after throw in your leftover veg from sunday lunch. Add some stock for flavour if needed (my DD doesn't have any). My DD wolfs this meal down and can never get enough of it. Eggs also are good in protein. The vegetarian society recommends this diet for young veggies:
Vegetables 2 servings preferably including leafy dark green types
Fruit 1 - 3 servings with dried fruit every few days
Grains/cereals 4 - 5 servings inculding wholegrain bread, rice, pasta, potatoes, breakfast cereals
Nuts, pulses, mashed beans and seeds 1 - 2 servings including nut butters, lentils,
Dairy or soya 3 servings including milk, cheese, hard boiled, free-range eggs, yoghurt, fortified soya milk, tofu,
HTH