Protein is very essential for muscle building and physical development of children. Therefore, include these protein-rich foods in your child's diet: Low-fat protein sources: Eggs, chicken, fish, beans, lentils, tofu and calcium-rich dairy products including milk, curd, ghee, butter, cream, and cheese. Complex carbohydrates: Whole grains such as brown rice, quinoa, and whole-wheat bread and potatoes provide sustained energy for exercise. Healthy Fats: Avocados, nuts, seeds and olive oil support overall health brain development and hormone regulation.