1. Introduction
n December 2019, the new coronavirus disease (COVID-19) was first identified in Wuhan, China, and then spread rapidly around the world, such that the World Health Organization reported it as a pandemic. In humans, COVID-19 mainly causes respiratory and gastrointestinal manifestations, ranging from a simple cold to severe clinical symptoms such as bronchitis, pneumonia, acute respiratory distress syndrome, disseminated intravascular coagulation, simultaneous organ failure, and death. Children can play an important role in transmitting the virus to the community. In some cases, the virus can even be spread through the stool for several weeks after diagnosis in infants. This study aims to review the epidemiological findings, transmission methods, clinical manifestations, radiological symptoms, prognosis and treatment of COVID-19 in children, as well as the differences caused by the virus between children and adults.
2. Materials and Methods
The search was conducted in databases such as PubMod, Scopus, ScienceDirect and Google Scholar on studies published from December 2019 to July 2020 by using the keywords “COVID-19”, “Coronavirus”, “Children”, and “Pandemic”. The initial search yielded 446 articles. After reading their abstracts and full texts, as well as deleting duplicate and similar articles and case reports, finally 26 articles related to COVID-19 in children were selected.
3. Results
With the increase in the number of cases worldwide, the prevalence of COVID-19 in children is certainly increasing. Most findings reported that the course of the disease is milder in children, and that infection with the virus in children has a better prognosis. Due to the mild clinical symptoms in children, many of them are not diagnosed in the early stages of the infection. On the other hand, in infants as well as children in pre-school age, the clinical manifestations of this disease are much more severe than in older children. Moreover, underlying lung disease and defective immune system cause more severe clinical symptoms in children. In a significant percentage of children with COVID-19 virus found in the respiratory system, there was a co-infection with other viruses. In some cases, the virus continues to spread through the stool for several weeks after diagnosis in children, and thus it can spread to kindergartens, elementary schools, or even homes. Clinical manifestations in children include gastrointestinal symptoms such as abdominal pain, nausea, diarrhea, and vomiting, which are more common than in adults.
4. Discussion and conclusion
Despite numerous studies on COVID-19 in adults, few studies have been conducted on children. The prevalence of the disease and the severity of its clinical symptoms are much lower in children than in adults and the disease usually has a better prognosis in children. Due to the lack of specific antiviral drugs and vaccines against this virus, the best way is to follow health standards. Given the certain characteristics of COVID-19 such as non-specific symptoms, transmission of the virus during the latency period, the tendency of the virus towards mucous membranes including the conjunctiva, the long course of the disease, and the possibility of transmission even after recovery, it is difficult to prevent from COVID-19.

Ethical Considerations
Compliance with ethical guidelines
Ethical principles have been observed according to the instructions of the National Ethics Committee and the COPE regulations.

Funding
This study was supported by Shahid Beheshti University of Medical Sciences. 

Authors' contributions
 The authors observed the criteria of the International Committee of Medical Journal Editors (ICMJE).

Conflicts of interest
The authors declare no conflict of interest.


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