A serving of dairy with lunch supplies your child with a healthy amount of calcium, a nutrient essential for his bones. Toddlers and preschoolers need 2 cups of milk or the equivalent each day. One cup of milk supplies your child with about one-third of the calcium he needs each day. Pack an individual serving of milk in a thermos or airtight cup. In addition to calcium, milk also contains vitamin D, a nutrient that enables your child's body to absorb calcium. Pack an ounce of cheddar cheese with crackers or put a slice of cheese on his sandwich. A serving of cottage cheese with fruit is another healthy way to add dairy to his lunchbox. A carton of yogurt is a nutritious source of calcium and supplies a small amount of protein as well.