Just over 1,000 cases have been recorded in 35 countries, according to the World Health Organization (WHO), and 22 deaths.
The majority of affected children are under the age of six, and some 5% of them have required liver transplants.
Both studies, which have not yet been peer-reviewed, concluded that a Covid-19 infection was not responsible.
The coronavirus was not detected in the livers of the sick children studied, and the proportion of them showing antibodies against Covid-19 was similar to that of children not affected by these hepatitis.
Conducted by scientists in Scotland and England respectively, these studies point to another culprit: a common virus called AAV2 (adeno-associated virus 2), detected at high levels in sick children.
This virus is not normally known to cause disease.
It cannot replicate itself, and needs another virus for this, an adenovirus, or more rarely the herpes virus (HHV6).
Researchers believe that the co-infection of two viruses (AAV2 and an adenovirus, or HHV6) is currently the best explanation for these cases of hepatitis.
"I think this is a plausible explanation for these cases," said Deirdre Kelly, a professor of pediatric hepatology at the University of Birmingham, who was not involved in these studies, in a statement.
"It seems that co-infection plays a key role."
"But it's still not understood why some children develop severe cases of the disease requiring a transplant. Could one possibility be co-infection with more than a virus?" she added.
Scientists also do not clearly understand why these cases are appearing precisely now.
One hypothesis is that the confinements linked to the coronavirus have had an influence, for example by modifying the usual circulation of other viruses, or by preventing children from creating certain defenses against viruses with which they have been less confronted.
© 2022 AFP