Development of the Immune System in Children

Everyone is born with an immune system. It consists of a team of cells, proteins, tissues and organs that fight off illness, germs and other invaders. When an unsafe substance enters the body, the immune system kicks into gear and attacks. In a baby's first few months, her immune system is not fully developed. Fortunately, humans are protected by antibodies passed on from their mother's placenta. Over the next several years, along with the brain and other organs, the immune system develops at a precise pace.

Origins of the Immune System

A baby is born with more defenses than you might expect, says Dr. Laura A. Jana, a board-certified pediatrician and fellow of the American Academy of Pediatrics (AAP). "During pregnancy," Jana notes, "disease-fighting antibodies made in the mother's immune system are able to make their way across the placenta and into her baby's body." These antibodies continue to protect a baby for several months after birth.

Baby’s First Few Months

As time goes by, a baby benefits less and less from his mother's immune system—unless he is breastfed. Mothers produce milk rich in cells that fight disease and infection, so breast milk continues to supplement a baby with disease-fighting antibodies long after delivery. Formula cannot duplicate the benefits of mother's milk. Comparatively, breastfed infants generally suffer from fewer chronic diseases, such as allergies, rheumatic disorders and ear infections.

Still, formula-fed babies do not have an immune system, it's just slower to develop. For instance, a formula-fed infant takes about a month to develop the antibodies necessary to fight serious disease. If antigens get into a child's system, her immune system may not fully develop a resistance to that bug; the newly developing immune system might incorrectly identify that strain of antigen as harmless.


At 2 to 3 months old, immunoglobulin antibodies passed on from the mother's placenta will be at a low point. This is when the baby's immune system begins producing its own antibodies.

To aid in kick-starting the immune system, infants are vaccinated against some diseases; vaccines essentially are tiny amounts of inactive, disease-causing bacteria.

In the magazine BabiesToday, Dr. F. Sessions Cole, director of newborn medicine at St. Louis Children's Hospital, notes: "Vaccinations teach an infant's immune system to recognize specific, highly contagious, dangerous germs that cause serious diseases (for example, polio, whooping cough and German measles)."


One of the best ways to help your 3- to 6-month-old continue building a healthy immune system is good nutrition. By this time, she should be eating some solids. Lauren Graf, clinical dietitian at the Montefiore Medical Center in New York, suggests feeding your child creamy sweet potatoes and applesauce. The vitamins, minerals and antioxidants in these foods protect the cells of the immune system. As your child grows and begins eating more solid foods, incorporate other nutrients, such as zinc, found in fortified cereals, beans and eggs, to keep her immune system functioning well.

Be aware that some foods can suppress an immature immune system, Graf says. So limit sugars from juice and other packaged foods, such as yogurt.


Researchers continue to explore all the ways sleep benefits our health, but what's known for sure is that older children who do not get enough sleep have a poorer response to the flu vaccine. Further, the study "Sleeping to Fuel the Immune System," written by doctors from the University of Michigan Medical School, indicate that the immune system is impaired by lack of sleep.

While newborns and infants can sleep anywhere from 16 to 20 hours a day, even your 3-year-old needs upwards of 10 to 14 hours a night and naps during the day, according to the National Sleep Foundation.

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