don't know on that. your first two statements only focus on US. Studies below along with commentary from NIH:
https://www.nejm.org/doi/pdf/10.1056/NEJMoa2006100?articleTools=true
Study published in the New England Journal of medicine showing infection rates for children 10 and under is half of what it is for people over 10 years old. This data come from Iceland’s screening of its population. Genetic sequence tracing.
https://www.sciencemuseumgroup.org.uk/blog/hunting-down-covid-19/
Commentary from the above study. “Children under 10 are less likely to get infected than adults and if they get infected, they are less likely to get seriously ill. What is interesting is that even if children do get infected, they are less likely to transmit the disease to others than adults. We have not found a single instance of a child infecting parents.”
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7268273/
Here is a study from Ireland which shows no evidence of secondary transmission of covid from children attending school. They tracked child contacts of cases and there were no confirmed secondary cases.
http://ncirs.org.au/sites/default/files/2020-04/NCIRS NSW Schools COVID_Summary_FINAL public_26 April 2020.pdf
A report on school-related transmission in New South Wales, Australia, examining the spread of SARS-CoV-2 from 18 confirmed cases (nine students and nine staff) from 15 schools identified only two potential cases of secondary school-based transmission, despite the identification of 863 close contacts
https://www.rivm.nl/en/novel-coronavirus-covid-19/children-and-covid-19
A study from the Netherlands. Essentially repeating the same.
https://pubmed.ncbi.nlm.nih.gov/32371442/
From the NIH explaining the children are not Covid spreaders.
https://www.npr.org/2020/06/24/882316641/what-parents-can-learn-from-child-care-centers-that-stayed-open-during-lockdowns
NPR article on tracking spread at the YMCA from children of essential workers.
“The YMCA says that during the lockdowns it cared for up to 40,000 children between the ages of 1 and 14 at 1,100 separate sites, often in partnership with local and state governments. And in New York City, the pandemic's national epicenter in March and April, the city's Department of Education reports that it cared for more than 10,000 children at 170 sites. Working in early days, and on very short notice, these two organizations followed safety guidance that closely resembles what's now been officially put out by the Centers for Disease Control and Prevention. The Y says a few staff members and parents at sites around the country did test positive, but there are no records of having more than one case at a site. This, among a population of essential workers.”