Despite an obesity epidemic in this country, nearly 4 percent of children and teens are underweight. Being underweight is not the same as being thin or slender. Some children have a naturally slight build and maintain it with a well-balanced diet and physical activity. However, true underweight may be a sign of dietary, health or emotional problems.

If you are concerned that your child may be underweight, consult your child’s physician. Assuming your child has no underlying medical concerns, the idea will then be to encourage weight gain in a healthful way, with food. Empty calories from foods high in fat and added sugars might add a few pounds, but they will not provide the nutrients a child needs to build strong bones and a healthy body.

If your child is underweight, start by ensuring that most meals and snacks are nutrient-rich. Good sources of protein for weight gain include eggs, peanut butter and other nut butters, bean soups, hummus and full-fat milk, yogurt and cheese. Whole wheat bread and pasta, mashed potatoes and hot cereal are excellent carbohydrate choices, while nuts and seeds, and avocados, are healthy fat sources to help your child gain weight.

When planning snacks, be sure they provide additional calories and great taste. Consider these healthy, higher-calorie foods:

• Make guacamole with fresh avocados, onions and tomatoes, or mix avocado into a fruit smoothie.
• Make a smoothie for an on-the-go breakfast or snack. Smoothies are an easy way to get nutrients plus calories. Get creative with your favorite fruit, full-fat yogurt, nut butters and seeds.
• Granola or trail mix made with nuts, seeds, dried fruit and chocolate chips can also be mixed with full-fat yogurt.
• Hummus and bean dips not only make good snacks, they are an excellent source of protein and fat.

Along with eating these foods, work to make mealtimes pleasant and not rushed. Involve your children in meal planning, shopping and food preparation to encourage their interest in food and eating. Doctors may recommend a high-calorie supplement drink for picky eaters who refuse to add new foods to their diet. Make sure, though, that your child isn't filling up on beverages, like juices or even milk, so that she's hungry at meal-time.

If your child is getting enough calories but still does not seem to be gaining weight appropriately, continue to work with her doctor to discover any underlying conditions. Chances are good, though, that with some patience and conscientious meal and snack plans, your child will strike a good height and weight balance.

Source: http://www.eatright.org/resource/health/weight-loss/your-health-and-your-weight/safe-weight-gain-tips-for-underweight-kids