Acute Lymphoblastic Leukemia (ALL) treatment often results in bone weakness due, in part, to Vitamin D insufficiency. The resultant large number of survivors from ALL have a significant possibility of suffering from poor bone health. It is felt that Vitamin D intervention during and after treatment can prevent this outcome. This is a randomized trial of vitamin D and calcium supplementation in vitamin D-insufficient subjects. Eligible patients will be identified at the Jonathan Jaques Children’s Cancer Center (JJCCC) and the MCH/PAHO outpatient clinic. There are two groups in this study: Group A: Newly diagnosed ALL patients and Group B: Off-therapy ALL patients. The intervention arm consists of vitamin D supplements administered once every two months in either the inpatient or outpatient settings, plus daily chewable calcium carbonate (Tums©) taken at home. For every two patients receiving the Vitamin D and calcium intervention, one patient will be followed as per standard of care (a “2:1 randomization”).