Anemia in children most often results from not getting enough iron, but it can also stem from inherited blood disorders, vitamin deficiencies, chronic illness, lead exposure, or conditions that destroy red blood cells faster than the body can replace them. The specific cause matters because it determines what a child needs, whether that’s a dietary change, a supplement, or a more targeted treatment.
Anemia means a child’s hemoglobin, the protein in red blood cells that carries oxygen, has dropped below the normal range for their age. What counts as “normal” shifts as children grow. A two-year-old is considered anemic below 10.5 g/dL, while a 12-year-old boy would need to fall below 13 g/dL to meet the threshold.
Iron Deficiency: The Most Common Cause
Iron deficiency accounts for the vast majority of childhood anemia cases. Children need a steady supply of iron to produce hemoglobin, and when intake falls short, their red blood cells become smaller and carry less oxygen. The CDC notes that children who do not get enough iron from food or supplements can develop anemia, and in young children this is the single most frequent cause.
The timeline of risk starts before birth. About 80 percent of a newborn’s iron stores are built up during the last three months of pregnancy, which means babies born prematurely often start life with a deficit. Full-term, healthy infants typically have enough stored iron for at least four months. After that, they need iron-rich foods or fortified formula to keep up with rapid growth.
Toddlers face a particular risk because of cow’s milk. Cow’s milk is low in iron and can irritate the gut lining in young children, causing tiny amounts of blood loss over time. A toddler who drinks large quantities of milk and eats few iron-rich foods like meat, beans, or fortified cereals can slide into deficiency quickly. The American Academy of Pediatrics recommends universal anemia screening at around 12 months of age, in part because this is the stage when iron stores from birth run out and dietary habits start to matter.
Even mild iron deficiency anemia can affect a child’s energy, focus, and ability to learn. Chronic iron deficiency, if left unaddressed, can result in long-term developmental impairment that may not fully reverse even after iron levels are restored.
Inherited Blood Disorders
Some children are born with genetic conditions that cause their red blood cells to break down prematurely or form abnormally. The two most common inherited causes of anemia are sickle cell disease and thalassemia.
In sickle cell disease, red blood cells become rigid and crescent-shaped, which makes them fragile. These misshapen cells rupture more easily than normal red blood cells, a process called hemolysis. When red blood cells break apart in the bloodstream, they release their contents into the plasma, triggering inflammation and reducing the availability of nitric oxide, a molecule that keeps blood vessels relaxed and open. The result is chronic anemia combined with pain crises and organ damage over time. Both sickle cell disease and thalassemia red blood cells also carry higher levels of damaging molecules called reactive oxygen species, which further shorten their lifespan.
Thalassemia works differently at a molecular level but produces a similar outcome: the body either makes too little hemoglobin or makes an abnormal version of it. Children with mild forms (thalassemia trait) may have only slightly low hemoglobin and need no treatment. More severe forms can require regular blood transfusions.
These conditions are inherited from both parents. They are more common in families with ancestry from sub-Saharan Africa, the Mediterranean, the Middle East, and Southeast Asia. Newborn screening programs in the United States catch sickle cell disease at birth, so most affected children are identified early.
Vitamin B12 and Folate Deficiency
Iron isn’t the only nutrient that matters. Children who are low in vitamin B12 or folate develop a different type of anemia called megaloblastic anemia, where the body produces abnormally large red blood cells that don’t function properly. Nationwide Children’s Hospital identifies inadequate B12 or folate as the most common cause of this type of anemia in children.
Restrictive diets are a frequent trigger. Children on strict vegan or vegetarian diets without supplementation are at risk for B12 deficiency, since B12 is found almost exclusively in animal products like meat, eggs, and dairy. Folate comes from leafy greens, legumes, and fortified grains, so children who are extremely picky eaters can fall short.
Digestive conditions also play a role. Celiac disease, chronic gut infections, and prior stomach or intestinal surgeries can all impair the body’s ability to absorb these vitamins even when a child eats enough of them. Some children have a condition called pernicious anemia, where the stomach fails to produce a protein needed to absorb B12. Certain seizure medications can also interfere with folate absorption.
Lead Exposure
Lead is a well-established cause of anemia in children, particularly those living in older housing with deteriorating lead paint or contaminated water. Lead directly interferes with the body’s ability to build hemoglobin by blocking key enzymes in the production pathway. Specifically, it shuts down the enzyme that inserts iron into the hemoglobin molecule, leaving behind incomplete building blocks that accumulate in red blood cells instead of becoming functional hemoglobin.
Children absorb lead far more efficiently than adults do, and even low-level exposure can contribute to anemia alongside its better-known effects on brain development. In neighborhoods where lead exposure remains a concern, anemia screening and lead testing often go hand in hand.
Chronic Illness and Inflammation
Children with long-standing inflammatory or chronic conditions can develop what’s known as anemia of chronic disease. The mechanism is different from nutritional deficiency. Ongoing inflammation causes the body to produce signaling molecules (cytokines) that suppress the production of erythropoietin, the hormone that tells bone marrow to make new red blood cells. Inflammation also locks iron away in storage, keeping it out of circulation even when the child’s overall iron levels are adequate.
Conditions that commonly trigger this type of anemia include juvenile arthritis, inflammatory bowel disease, lupus, and chronic kidney disease. In kidney disease specifically, the damaged kidneys produce less erythropoietin directly, which slows red blood cell production at the source. Treating the underlying disease typically improves the anemia, though some children need additional support.
Red Blood Cell Destruction From Immune Problems
In autoimmune hemolytic anemia, a child’s immune system mistakenly attacks and destroys its own red blood cells. This can happen on its own or alongside another condition such as Epstein-Barr virus infection, lupus, immunodeficiency disorders, or ulcerative colitis. The onset can be sudden, with a child becoming pale and fatigued over days rather than weeks.
Children whose red blood cells are being destroyed may develop jaundice, a yellowing of the skin and eyes, along with dark tea-colored urine. These signs are distinct from the slow, gradual pallor of iron deficiency and usually prompt faster evaluation.
Signs to Watch For
Mild anemia often looks like tiredness. A child may seem more irritable than usual, nap more frequently, or lose interest in play. Skin may appear paler than normal, and the lining inside the lower eyelid or the nail beds may look less pink.
As anemia worsens, more noticeable symptoms appear: shortness of breath, a rapid heartbeat, dizziness, headaches, and swollen hands or feet. Some children develop restless leg syndrome. One particularly distinctive sign of severe iron deficiency is pica, a craving for non-food items like ice, dirt, clay, paper, or cornstarch. Pica is not just a quirky habit; it’s a recognized signal that a child’s iron levels are very low and can itself cause constipation and other complications.
Because the normal hemoglobin range changes with age, what looks like a normal result at one age could signal anemia at another. Newborns naturally have high hemoglobin (the cutoff is 13.5 g/dL), which drops to its lowest point around two months (9.4 g/dL) before gradually climbing again through childhood. This normal dip, sometimes called physiologic anemia of infancy, is not the same as disease and doesn’t require treatment in otherwise healthy babies.