Underweight 10-Year Old

What methods can be recommended for putting some meat on his bones?  He is very active but never seems to really be hungry.  We feed him well-balanced meals to ensure he's getting as much nutrition as possible.  It's just so disconcerting to be able to (practically) count his ribs...

Any advice is appreciated.  Thank you.

[Renee Radenberg]

His weight is on the 5th percentile and his height is just below the 50th percentile for his age. That is good you give him well balanced meals. Suggest giving him milk shakes (milk, ice, cream, and fruit blended) or yogurt smoothies (yogurt, fruit, and ice cream blended) at each meal for additional calories and protein for weight gain. Make sure he is eating a protein food each meal (meat, fish, cheese, or yogurt) too. Some tips for additional calories: If he likes pasta, then add meat or cream sauces to the pasta instead of plain tomato sauce or plain pasta. Add dry milk to oatmeal, mashed potatoes, gravies, creamed vegetables, and creamed soups (add additional meats to soups). Hoped this helped you.