There is no perfect or ideal weight for a 4-year-old boy. Weight is related to height and body composition rather than age. In General a growing boy needs diet which is rich in protein. He also needs simple carbs for energy expenditure. Fats are needed for the absorption of fat soluble vitamins and they also need vitamins and minerals such as calcium.The caloric requirement will depend on his activity. If he is gaining weight noramlly and is healthy and happy he should have no problems. A balanced diet an physical activity will help him to create a strong mind and body. You can also visit our nutrition section for more details about food types. Good Luck Good