Reed Mangels, a nutrition adviser for the Vegetarian Resource Group, said such conflicts are an opportunity to practice tolerance, learning how to live with and get along with people of differing viewpoints.

Susan Levin, director of nutrition education for the Physicians Committee for Responsible Medicine, a nonprofit that promotes a plant-based diet, said studies show that vegetarian children and teens are at lower risk than their nonvegetarian peers for being overweight and obese — conditions that are linked to Type 2 diabetes and heart disease.

A child can get all the necessary nutrients in a vegetarian diet through a variety of foods like grains, soy, vegetables, fruits, nuts and beans, according to the American Academy of Pediatrics. Nutritionally balanced vegetarian diets are more challenging if a child is more selective, “but there are picky vegetarians who are healthy,” said Ms. Passerrello. The American Academy of Pediatrics recommends that parents consult a trained dietitian for an individual assessment and recipe recommendations.

One of the biggest myths about vegetarian diets is that they lack sufficient protein. “On average, most kids consume far more protein than they need,” says Ms. Levin. According to the National Academy of Medicine, those ages 9 to 13 need 34 grams of protein a day. A cup of tofu contains seven grams, while a cup of cooked beans has 15 grams, as does a cup of soy milk. A mere tablespoon of peanut butter contains roughly four grams.

Parents do need to be vigilant in ensuring vegetarian children get enough of one essential nutrient: iron. Ms. Passerrello said that iron is more easily absorbed from animal sources than plants. Spinach and whole grains are the best vegetarian sources. She said iron is better absorbed in plant-based sources when combined with vitamin C, so squeezing lime, lemon or orange on a salad or adding citrus fruits to smoothies can be helpful. Cereals fortified with iron are another option.

Vegan diets are slightly more challenging than vegetarian. The only essential nutrient found in animal products that is not usually found in plants is vitamin B12. While vegetarians can get that through dairy products, vegans cannot. So it’s typically recommended that vegans take a B12 supplement or consume foods fortified with vitamin B12. Dr. Mangels points out that B12 is often added to soy milk, veggie meats and some breakfast cereals. Vegans can consume fortified plant milk to get calcium found in cow’s milk, along with high calcium foods like dark green vegetables, she said.