In December 2019, the emergence of a novel coronavirus, which rapidly turned into a pandemic that posed a public health threat of global concern and has had a huge impact on the health of millions of people around the world. Existing evidence indicates relatively low incidence and mild severity of coronavirus disease 2019 (COVID-19) in children compared with adults; although the precise underlying reasons for such disparity remain obscure. The article provides general information about COVID-19 and epidemiological data of the disease in children, its clinical manifestations and multisystem inflammatory syndrome in children. The main aim of this article is to explore the reasons given for the mildness of the disease in pediatric patients. Several theories related to immunosenescence, vaccination and trained immunity, co-infection, angiotensin-converting enzyme-2 maturation and expression, viral exposure, overall health and smoking have been proposed in recent literature. However, due to the novelty of this virus and the lack of information about it, these reasons are not conclusive; however, these points are considered as possible reasons for the low prevalence and mildness of the disease in pediatric patients.