The purpose of this study is to evaluate the safety and pharmacokinetics (drug levels in the blood) of teplizumab in children less than 8 years old. The study will also assess if your child stays in Stage 2 T1D or progresses to Stage 3 T1D. Your child may join the study only if they are in Stage 2 T1D. Previous studies in adults and children older than 8 years of age suggest that taking teplizumab, a drug that affects your childs immune system, may stop, delay, or decrease the attack on the cells that make insulin. This slowing or blocking of the immune attack may reduce the risk of short-term and long-term consequences of T1D. To join this study, your child must have been diagnosed with Stage 2 T1D based on two positive T1D-related antibodies and confirmed dysglycemia (abnormal blood sugar levels) based on an oral glucose tolerance test, fasting plasma glucose test, or an increase in a blood test called the hemoglobin A1c. The study is open-label. That means that if your child qualifies for the study, your child will receive teplizumab. There is no placebo in this study.