On 31 March 2022, Scotland first reported five children with unexplained severe hepatitis. The World Health Organization (WHO) issued a guidance on April 15, defining confirmed cases, possible cases and epidemic-related cases of the unexplained hepatitis affecting children. As of April 21, 169 confirmed cases, whose ages ranged from 1 month to 16 years, had been reported in 12 countries. The clinical manifestation was acute hepatitis with aspartate aminotransferase (AST) or alanine aminotransferase (ALT) above 500 IU/L. Many cases had jaundice, nausea, abdominal pain, fatigue, sleepiness and gastrointestinal symptoms like diarrhea and vomiting. Most cases had no fever. Seventeen cases received liver transplantation and at least one death was reported. Considering the epidemiological and clinical characteristics of the cases, infectious factor(s) is more likely to be the etiology. The laboratory examination results of all cases excluded hepatitis A, B, C, D and E, while suggested adenoviruses may be related to the unexplained hepatitis in children, but other infectious factors or environmental factors cannot be completely ruled out. The present paper introduces the development and possible causes of the emerging unexplained hepatitis in children. China should be prepared to cope with an imported risk of this disease.