A 6-year-old boy from urban Delhi presents with his mother who reports poor school performance, irritability, and pica (eating mud and chalk) for 8 months. He attends a municipal school and lives in a 1-room tenement. On examination: height 105 cm (< 5th percentile for age), pallor present, no jaundice or hepatosplenomegaly. Developmental milestones: speech delayed by 6 months, fine motor skills lag. Laboratory: Hb 9.8 g/dL, MCV 68 fL, serum ferritin 12 ng/mL, serum iron 28 µg/dL, TIBC 380 µg/dL. Lead level 18 µg/dL (normal < 10). Stool examination: no hookworm ova. What is the primary concern regarding this child's long-term outcome if iron deficiency is not corrected promptly?