Serve plenty of finger foods. Utensils can frustrate toddlers and make them less interested in a meal. Let your son set up his own plate. It really matters to toddlers where the potato is placed and where the lentils go. In addition, there are a few other things to consider in feeding vegetarian children.
Vegetarian children have diets that are much higher in fiber than non-vegetarian children.
While this has some definite lifelong health benefits, fiber is very filling and can cause young children to feel full without eating enough calories. So, do include some lower-fiber foods in your son's diet. Try peeling fruits or offering some canned fruits, and offer some refined grains like pasta or white bread. You can make sandwiches using one slice of white bread and one of whole wheat. Offer some juices to help meet calorie and nutrient needs but don't over-do it with these foods.