Neither change in linear growth from 18 months to 4–6 years nor Hb at age 4–6 years were associated with cognition at 4–6 years, which suggests that the brain may not be as vulnerable during this period to environmental exposures that cause both linear growth faltering or low Hb and long term cognitive deficits as compared with the first 1,000‐day window. This evidence concerns the gene GSTM1 and Cognitive impairment.