Young children should consume about 800 milligrams of calcium a day. But between ages 9 and 18, when bone growth speeds up, that requirement almost doubles to 1,300 mg. That's about three cups of fat-free or low-fat milk plus additional calcium-rich foods, such as broccoli, cheese, yogurt, or calcium-fortified orange juice.
Children and adolescents need at least 200 international units of vitamin D.
Milk and orange juice often is fortified with the vitamin and a few other foods contain it. Sunlight is a major source. About 10 to 15 minutes of sun exposure weekly is enough for many children, although skin pigmentation alters sun absorption so black children need more. The goal is to get just enough sun for vitamin D production while avoiding too much of its skin-damaging rays.
Children of all ages need about an hour of physical activity most days, and 10 to 15 minutes at a time can add up. Weight-bearing exercises strengthen bone, anything from team sports like soccer to simply jumping rope or running around. The goal is for the arms or legs to bear all the body's weight.