Vitamin D is critical for bone health and also plays a role in immunity. But many US infants and toddlers aren't getting enough vitamin D. According to research from the Children's Hospital in Boston, a full 40% aren't getting the appropriate amount of vitamin D.

Breast milk doesn't contain high quantities of vitamin D, so if you're breastfeeding your infant ask your doctor if supplementing the vitamin is a good idea. Toddlers can benefit from vitamin D-fortified milk. Perhaps the best source of vitamin D is sunlight. While it's, of course, important to protect your child's skin, some exposure to sunlight is healthful as it triggers the production of vitamin D in the body.