This study is being done to find out how accurate the Navigator continuous glucose monitor is in children. It is also being done to see if use of the Navigator can improve blood sugar control and help prevent low blood sugar events. This study has three basic parts: Use of the Navigator at home for one week without being able to see the blood sugar readings; a Baseline visit or a 24-hour admission to a research unit of the hospital to find out how well the Navigator measures the blood sugar; and then 3 months use of the Navigator at home as an aid to diabetes care.