We expect to see on average about 8 new patients per week and we expect that at least 50% of them will have vitamin D level below 21 ng/mL and will be between the ages of 5 and 11 years. Over two years that amounts to 416 prospective study subjects. Dosages selected are based on the Endocrine Society Clinical Practice Guidelines (2011), which state that children with vitamin D deficiency should be treated with 2000 IU of vitamin D once a day; however obese children should be treated with 2-3 times that amount. In total we expect to enroll 192 subjects over two years to the intervention portion of this trial (5 - 11 years) and we expect to enroll a total of 400 subjects to the observational portion (prevalence and associations with lab testing).