[M T]

I am a firm believer in following the data.  If analysis of COVID-19 transmission to date had shown that there has been frequent spread of COVID-19 in in-person or hybrid school settings (and that the adult family members were getting sick from their kids), I would be much more hesitant towards endorsing in person classes, but the data is supportive of cautiously restarting in person classes.  The risks will never be zero, but in this case they are low enough and substantially outweighed by the benefits.

I don't know what you define as "frequent".   You mention data.  Can you please share that data?

Transmission Dynamics of COVID-19 Outbreaks Associated with Child Care Facilities - Salt Lake City, Utah, April-July 2020

To better understand transmission from young children, contact tracing data collected from three COVID-19 outbreaks in child care facilities in Salt Lake County, Utah, during April 1-July 10, 2020, were retrospectively reviewed to explore attack rates and transmission patterns. A total of 184 persons, including 110 (60%) children had a known epidemiologic link to one of these three facilities. Among these persons, 31 confirmed COVID-19 cases occurred; 13 (42%) in children
...
Transmission was documented from these children to at least 12 (26%) of 46 nonfacility contacts (confirmed or probable cases). One parent was hospitalized. Transmission was observed from two of three children with confirmed, asymptomatic COVID-19.

The children were median age = 7 years; range = 0.2–16 years.

Of the 184 with links, half were asymptomatic & not tested.  I didn't see how many of the 110 children weren't tested. It is possible some cases were not detected.

13 of 110 children got infected, more than 10%.  R was approximately 1 for those children passing it on to others.

Contact Tracing during Coronavirus Disease Outbreak, South Korea, 2020

We analyzed reports for 59,073 contacts of 5,706 coronavirus disease (COVID-19) index patients reported in South Korea during January 20–March 27, 2020. Of 10,592 household contacts, 11.8% had COVID-19. Of 48,481 nonhousehold contacts, 1.9% had COVID-19.
... We grouped index patients by age: 0–9, 10–19, 20–29, 30–39, 40–49, 50–59, 60–69, 70–79, and >80 years.
... We detected COVID-19 in 11.8% of household contacts; rates were higher for contacts of children than adults. These risks largely reflected transmission in the middle of mitigation and therefore might characterize transmission dynamics during school closure (3). Higher household than nonhousehold detection might partly reflect transmission during social distancing, when family members largely stayed home except to perform essential tasks, possibly creating spread within the household.
...We also found the highest COVID-19 rate (18.6% [95% CI 14.0%–24.0%]) for household contacts of school-aged children and the lowest (5.3% [95% CI 1.3%–13.7%]) for household contacts of children 0–9 years in the middle of school closure. Despite closure of their schools, these children might have interacted with each other, although we do not have data to support that hypothesis. A contact survey in Wuhan and Shanghai, China, showed that school closure and social distancing significantly reduced the rate of COVID-19 among contacts of school-aged children

Adolescent with COVID-19 as the Source of an Outbreak at a 3-Week Family Gathering — Four States, June–July 2020
13yo brings home COVID from a day camp.  Negative  Only symptom was a stuffy nose 2 days after a negative antigen test (4 days after exposure).  11 subsequent cases.  One hospitalized; another sought ER treatment.

[M T]

I am a firm believer in following the data.  If analysis of COVID-19 transmission to date had shown that there has been frequent spread of COVID-19 in in-person or hybrid school settings (and that the adult family members were getting sick from their kids), I would be much more hesitant towards endorsing in person classes, but the data is supportive of cautiously restarting in person classes.  The risks will never be zero, but in this case they are low enough and substantially outweighed by the benefits.

I don't know what you define as "frequent".   You mention data.  Can you please share that data?

Transmission Dynamics of COVID-19 Outbreaks Associated with Child Care Facilities - Salt Lake City, Utah, April-July 2020

To better understand transmission from young children, contact tracing data collected from three COVID-19 outbreaks in child care facilities in Salt Lake County, Utah, during April 1-July 10, 2020, were retrospectively reviewed to explore attack rates and transmission patterns. A total of 184 persons, including 110 (60%) children had a known epidemiologic link to one of these three facilities. Among these persons, 31 confirmed COVID-19 cases occurred; 13 (42%) in children
...
Transmission was documented from these children to at least 12 (26%) of 46 nonfacility contacts (confirmed or probable cases). One parent was hospitalized. Transmission was observed from two of three children with confirmed, asymptomatic COVID-19.

The children were median age = 7 years; range = 0.2–16 years.

Of the 184 with links, half were asymptomatic & not tested.  I didn't see how many of the 110 children weren't tested. It is possible some cases were not detected.

13 of 110 children got infected, more than 10%.  R was approximately 1 for those children passing it on to others.

Contact Tracing during Coronavirus Disease Outbreak, South Korea, 2020

We analyzed reports for 59,073 contacts of 5,706 coronavirus disease (COVID-19) index patients reported in South Korea during January 20–March 27, 2020. Of 10,592 household contacts, 11.8% had COVID-19. Of 48,481 nonhousehold contacts, 1.9% had COVID-19.
... We grouped index patients by age: 0–9, 10–19, 20–29, 30–39, 40–49, 50–59, 60–69, 70–79, and >80 years.
... We detected COVID-19 in 11.8% of household contacts; rates were higher for contacts of children than adults. These risks largely reflected transmission in the middle of mitigation and therefore might characterize transmission dynamics during school closure (3). Higher household than nonhousehold detection might partly reflect transmission during social distancing, when family members largely stayed home except to perform essential tasks, possibly creating spread within the household.
...We also found the highest COVID-19 rate (18.6% [95% CI 14.0%–24.0%]) for household contacts of school-aged children and the lowest (5.3% [95% CI 1.3%–13.7%]) for household contacts of children 0–9 years in the middle of school closure. Despite closure of their schools, these children might have interacted with each other, although we do not have data to support that hypothesis. A contact survey in Wuhan and Shanghai, China, showed that school closure and social distancing significantly reduced the rate of COVID-19 among contacts of school-aged children

Adolescent with COVID-19 as the Source of an Outbreak at a 3-Week Family Gathering — Four States, June–July 2020
13yo brings home COVID from a day camp.  Negative  Only symptom was a stuffy nose 2 days after a negative antigen test (4 days after exposure).  11 subsequent cases.  One hospitalized; another sought ER treatment.