The pre-school years are critical years for children to acquire early learning skills such as language, fine motor and social skills; this is termed early child development. Primary care doctors (family doctors and pediatricians) are in a unique position to identify children with health or developmental problems. Screening is the process of testing healthy people for the earliest signs of health problems, followed by treatment, with the expectation that screening will improve the health of those screened. The focus of this research is screening young children for the earliest signs of iron deficiency (low blood iron levels) followed by treatment with oral iron.

Previous research has shown that children with later stages of iron deficiency have serious delays in their development. Some research has shown that these delays may persist into young adulthood often with a significant reduction in intelligence. Early stages of iron deficiency may be difficult for parents or doctors to detect, and a blood test is usually needed. However, Canadian guidelines do not recommend screening all children for iron deficiency, because there is not enough good quality research to prove that screening is effective.

In this study, the investigators will ask parents to allow their child between the ages of 1 to 3 years to have a blood test for iron levels. If the blood level is low, the child will be randomly assigned to receive either oral iron liquid for 4 months plus diet counseling, or a placebo liquid plus diet counseling. A psychologist will measure each child's early learning ability before and after the treatment. If this approach to screening children's blood iron levels followed by treatment improves children's development, parents and doctors may consider that routine blood screening tests are justified. Overall, this research is an important step to improving the ways in which primary care doctors can ensure that children have the best start to life-long health and achievement.

Inclusion Criteria:

• Age between 12 and 40 months attending any well child visit
• Informed parental consent

Exclusion Criteria:

• developmental disorder
• genetic, chromosomal or syndromic condition
• chronic medical condition (with the exception of asthma and allergies)
• chronic anemia, iron deficiency, or recent oral iron supplementation or treatment
• prematurity, with a gestational age of less than 35 weeks
• low birth weight less than 2,500 g;
• attending the office for an acute illness, such as a viral illness, or other health concern other than for a well-child assessment
• any contraindications to receiving elemental iron
• the use of any natural health product containing the same medicinal ingredient(s) as the investigational product
• English is not spoken to the child in the home or in a child care setting
• CRP level ≥10 mg/L

4 months

For children with NAID enrolled in the RCT, limitations include: our study population with high maternal education; our end points may not have been long enough; we were not able to measure chronicity of iron deficiency; the effect estimate for our primary outcome was based on findings from previous iron studies, but there is uncertainty regarding what is considered a meaningful treatment effect

The research pharmacy prepared ferrous sulfate and placebo in bottles of similar appearance and weight. The placebo was developed by the research pharmacy, was similar in color and consistency to the active agent, and had a distinctive taste.

Individuals masked to group allocation throughout the study included parents, attending physicians, research assistants, study personnel conducting outcome assessments, data analysts, and investigators. The biostatistician was unmasked after completion of data collection and locking of the database. The principal investigator was unmasked after the analysis.