Diabetes mellitus in children is defined as diabetes mellitus that occurs under the age of 15 years, and more than 90% of them are type 1 diabetes mellitus, but there is an increasing trend of type 2 diabetes mellitus due to the increasing obesity in children year by year. Type 1 diabetes is insulin-dependent diabetes, which means that the pancreatic islets of children are damaged and insulin secretion is reduced. The onset of the disease is generally rapid, and the symptoms may include weakness, excessive drinking, polyuria, increased nocturia, easy hunger, lethargy, etc. Some children may only show mental depression or an unexplained decline in academic performance. The cause is unknown and may be related to immunity, infection, and environmental factors. Type 2 diabetes mellitus, that is, insulin non-dependent diabetes mellitus, does not reduce insulin, or even increase insulin in these children. The onset of the disease in childhood is basically due to obesity. The onset of insidious, often due to improper diet, such as: do not eat breakfast, hungry, full, high sugar and high fat diet, like to eat snacks, etc.; reduced activity, such as: long hours of homework, watching TV, playing computer, etc.. The result is more intake and less consumption, which leads to weight gain, increased waist circumference, fatty liver, hyperlipidemia, abnormal liver function, hypertension, diabetes, etc. The basis of treatment is diet control and exercise, followed by oral medication and insulin injection. In terms of diet control, we should not only limit the total calories to avoid overnutrition, but also pay attention to balanced nutrition to meet the needs of children’s growth and development. Obese children should visit the endocrine clinic once every three months to six months for follow-up examinations of height, weight, blood pressure, liver function, blood lipids, blood sugar, insulin, etc. for early detection of diabetes. Diet and childhood diabetes are inextricably linked, but this does not just mean dieting, but that one should eat healthily. Just as children should not always drink beverages such as soda, lemonade or iced tea, they need to drink plain water and have a balance of meat and vegetables at each meal. In terms of exercise, the development of technology has caused children to gradually lose their basic physical exercise. They no longer walk or ride bicycles to their friends’ houses because they can be contacted by email or cell phone text messages. They no longer go outside to play together, but play computer games together. But the fact is that children need physical activity, and proper physical activity is essential for both physical development and intellectual development.