(1) Moderate or severe ALRI (using IMCI criteria) (2) Moderate or severe diarrhea (history of loose stools >3 times per day and history of oral rehydration or intravenous fluid therapy) (3) Incidence of hospital admissions for any illness; (4) Anthropometric indices at 0, 6, 12, 18 months (weight for height, weight for age, and height for age, head circumference) (5) All cause mortality and pneumonia specific mortality; (6) Biochemical markers of vitamin D deficiency [proportion of children with 25-OHD3 (cholicalciferol) <8ng/ml]38 at week 6 post vitamin D doses three (mid-spring) and four (mid-summer) in a random sample of 50 children each from the intervention and placebo group [We assume that the proportion of children with vitamin D deficiency will be 60% in the placebo group and it will be reduced to 30% in the intervention group at post vitamin D doses 3 and 4.]; (7) Pharmacodynamics of vitamin D supplementation will be determined by measuring serum 25-OHD3 (cholicalciferol) at day 2, week 6 and week 12 post vitamin D dose one in a random sample of 50 children each from the intervention and placebo groups] (8) The Thacher Radiological Score of Rickets 1 through wrist radiography of 10% random sample of children at the end of the 18 month follow up period.