Skimping on protein can retard growth and development, decrease immunity, weaken the heart and lungs and sap the energy that babies and toddlers need to play and learn. Every cell in the body contains protein, it makes up enzymes needed for chemical reactions and 10 percent of a child’s energy comes from protein. Dietary proteins are digested into amino acids that are used to make body proteins to grow and maintain the bones, muscles, blood, skin, hair and organs.