A 6-year-old boy from rural Bihar presents with bowing of legs, delayed tooth eruption, and frontal bossing. Serum calcium is 7.2 mg/dL, phosphate 3.8 mg/dL, and alkaline phosphatase 180 IU/L. A 35-year-old woman from the same village presents with bone pain, muscle weakness, and a serum calcium of 7.8 mg/dL, phosphate 3.2 mg/dL, and alkaline phosphatase 95 IU/L. Which feature best distinguishes nutritional rickets in the child from osteomalacia in the adult?