A 5-year-old boy from urban Delhi presents with poor school performance and lethargy. His hemoglobin is 9.8 g/dL with MCV 68 fL, serum ferritin 12 ng/mL, and serum iron 35 µg/dL. His mother reports he drinks 1.5 liters of cow's milk daily and eats little meat or vegetables. What is the most appropriate next step in management?